Twenty-nine people died as a result of the attack and approximately 220 people were injured. The attack was described by the BBC as "Northern Ireland's worst single terrorist atrocity" and by British Prime Minister Tony Blair as an "appalling act of savagery and evil". Sinn Féin leaders Gerry Adams and Martin McGuinness condemned the attack and the RIRA itself.
The victims included people from many different backgrounds — Protestants, Catholics, a Mormon, nine children, a woman pregnant with twins, two Spanish tourists, and other tourists on a day trip from the Republic of Ireland. The nature of the bombing created a strong international and local outcry against the RIRA, which later forced the organisation to apologise, and spurred on the Northern Ireland peace process. In 2001, County Louth builder and publican Colm Murphy was convicted in connection to the bombing. He is currently awaiting a Court of Criminal Appeal ordered retrial. Murphy's nephew Sean Hoey of Jonesborough, South Armagh was cleared of all charges relating to the bombing on 20 December 2007 after spending four years in prison on remand. The families of those killed say that they will continue with a High Court civil action for £14 million against the two men and three others whom they say were responsible for the attack.
That morning, three phone calls had been placed warning of an attack in Omagh. At 14:32, a warning was telephoned to Ulster Television saying "There's a bomb, courthouse, Omagh, main street, , explosion 30 minutes." The office received a second warning saying "Bomb, Omagh town, 15 minutes" one minute later. The next minute, the Coleraine office of the Samaritans charity received a call stating that a bomb would go off on "main street" about from the courthouse. The recipients passed on the information to the Royal Ulster Constabulary (RUC).
BBC News stated that the police "were clearing an area near the local courthouse, 40 minutes after receiving a telephone warning, when the bomb detonated. But the warning was unclear and the wrong area was evacuated." The warnings mentioned "main street" when no actual "Main Street" existed in Omagh at that time, although Market Street was the main shopping street in the town. The nature of the warnings led the police to move people over to the area where the bomb was actually placed. The courthouse is roughly 400 meters from the spot where the car armed with the explosive device was parked.
In a statement on the same day as the bombing, RUC Chief Constable Ronnie Flanagan accused the RIRA of trying to deliberately direct civilians to the bombing site. British government prosecutor Gordon Kerr QC has called the warnings "not only wrong but... meaningless" and stated that the nature of the warnings made it inevitable that the evacuations would lead to the bomb site. The RIRA has strongly denied that they intended to target civilians. They have also stated that the warnings were not intended to lead people to the bombing site. During the 2003 Special Criminal Court trial of RIRA director Michael McKevitt, witnesses for the prosecution stated that the inaccurate warnings were accidental.
The day after the bombing, the relatives and friends of the dead and injured used the Omagh leisure center to post news. The Spanish Ambassador to Ireland personally visited some of the injured and churches across Northern Ireland called for a national day of mourning. Church of Ireland Archbishop of Armagh Robin Eames stated on BBC Radio that \"From the church's point of view, all I am concerned about are not political arguments, not political niceties. I am concerned about the torment of ordinary people who don't deserve this.\"
Sinn Féin councillor Sean Clarke was the chairman of Omagh District Council. Within hours of the attack he was interviewed by UTV's Mark McFadden and said "It was murder... I utterly condemn it." Sinn Féin leader Martin McGuiness later stated that "This appalling act was carried out by those opposed to the peace process". Party president Gerry Adams said that "I am totally horrified by this action. I condemn it without any equivocation whatsoever." Martin McGuiness mentioned the fact that both Catholics and Protestants alike were injured and killed, saying "All of them were suffering together. I think all them were asking the question 'Why?', because so many of them had great expectations, great hopes for the future." Sinn Féin as an organization initially refused to co-operate with the investigation into the attack, citing the involvement of the Royal Ulster Constabulary. On 17 May 2007, Martin McGuiness stated that Irish republicans will cooperate with an independent, international investigation if one is created.
On 22 August 1998, the Irish National Liberation Army called for a ceasefire in their operations against the British government. The Terrorism Knowledge Base has accused the republican paramilitary organization of providing supplies for the bombing. The INLA has continued to observe the ceasefire and remains opposed to the Belfast Agreement. The RIRA also suspended operations for a short time after the Omagh bombing before returning to violence. The RIRA had came under pressure from the Provisional Irish Republican Army after the bombing; PIRA members visited the homes of 60 people connected with the RIRA and ordered them to disband and stop interfering with PIRA arms dumps. BBC News has stated that "Like the other bombings in the early part of 1998 in places like Lisburn and Banbridge, Omagh was a conscious attempt by republicans who disagreed with the political strategy of Gerry Adams and Martin McGuinness, to destabilise Northern Ireland in that vulnerable moment of hope. It failed - but there is a terrible irony to the way in which the campaign was halted only by the wave of revulsion triggered by the carnage at Omagh."
On 9 October 2000, the BBC's Panorama programme aired the special Who Bombed Omagh? hosted by journalist John Ware. The programme quoted RUC Chief Constable Ronnie Flanagan as saying "sadly up to this point we haven't been able to charge anyone with this terrible atrocity". The programme alleged that the police on both sides of the Irish border knew the identity of the bombers. It stated that "As the bomb car and the scout car headed for the border, the police believe they communicated by mobile phone. This is based on an analysis of calls made in the hours before, during and after the bombing. This analysis may prove to be the key to the Omagh bomb investigation." Using the phone records, the programme gave the names of the four prime suspects as Oliver Traynor, Liam Campbell, Colm Murphy, and Seamus Daly.
Northern Ireland Secretary Peter Mandelson praised the Panorama programme, calling it "a very powerful and very professional piece of work". Republic of Ireland Prime Minister Bertie Ahern criticised it, saying that "bandying around names on television" could hinder attempts to secure convictions. First Minister David Trimble stated that he had "very grave doubts about" it. Lawrence Rush, whose wife Elizabeth died in the bombing, tried to legally block the programme from being broadcast, saying "This is media justice, we can't allow this to happen". Democratic Unionist Party assembly member Oliver Gibson, whose niece Esther died in the bombing, stated that the government did not have the will to pursue those responsible and welcomed the programme.
The police believe that the bombing of BBC Television Centre in London on 4 March 2001 was a revenge attack for the broadcast. On 9 April 2003, the five RIRA members behind the BBC office's bombing were convicted and sentenced for between 16 and 22 years.
On 22 September 1998, the RUC and Irish police arrested twelve men in connection with the bombing. They subsequently released all of them without charge. On 25 February 1999, they questioned and arrested at least seven suspects. Builder and publican Colm Murphy, from Ravensdale, County Louth, was charged three days later for conspiracy and was convicted on 23 January 2002 by the Republic's Special Criminal Court. He is, as of January 2008, the only person ever convicted in connection with the explosion. He was sentenced to fourteen years. In January 2005, Murphy's conviction was quashed and a retrial ordered by the Court of Criminal Appeal, on the grounds that two Gardaí had falsified interview notes, and that Murphy's previous convictions were improperly taken into account by the trial judges.
On 28 October 2000, the families of four children killed in the bombing-- James Barker, 12, Samantha McFarland, 17, Lorraine Wilson, 15, and 20-month-old Breda Devine-- launched a civil action against the suspects named by the Panorama programme. On 15 March 2001, the families of all twenty-nine people killed in the bombing launched a £2 million civil action against the RIRA itself as well as suspects Seamus McKenna, Michael McKevitt, Liam Campbell, Colm Murphy, and Seamus Daly as individuals. Former Northern Ireland secretaries Peter Mandelson, Tom King, Peter Brooke, Lord Hurd, Lord Prior, and Lord Merlyn-Rees signed up in support of the plaintiffs' legal fund. The civil action began in Northern Ireland on 7 April 2008.
On 6 September 2006, Murphy's nephew Sean Hoey, an electrician from Jonesborough, County Armagh went on trial accused of 29 counts of murder, and terrorism and explosives charges. Upon its completion, Hoey's trial found on 20 December 2007 that he was not guilty of all 56 charges against him.
On 24 January 2008, former Chief Constable Ronnie Flanagan apologised to the victims' families for the lack of convictions in relation to the Omagh bombing.This apology was rejected by some of the victims' families. After the verdict freeing Sean Hoey, BBC News reporter Kevin Connolly stated that "The Omagh families were dignified in defeat, as they have been dignified at every stage of their fight for justice. Their campaigning will go on, but the prospect is surely receding now that anyone will ever be convicted of murdering their husbands and brothers and sisters and wives and children."
Initially, the Police Association, which represents both senior officers and rank and file members of the Northern Ireland police, went to court to try to block the release of the O'Loan report. The Association stated that "The ombudsman's report and associated decisions constitute a misuse of her statutory powers, responsibilities and functions." The group later dropped its efforts. RUC Chief Constable Ronnie Flanagan called the report "grossly unfair' and "an erroneous conclusion reached in advance and then a desperate attempt to find anything that might happen to fit in with that". Other senior police officers also disputed the report's findings. Flanagan issued a 190 page counter-report in response and has also stated that he has considered taking legal action. He has argued that the multiple warnings were given by the RIRA to cause confusion and lead to a greater loss of life. Assistant Chief Constables Alan McQuillan and Sam Kincaid sent affidavits giving information that supported the report.
The families of the victims expressed varying reactions to the report. Kevin Skelton, whose wife died in the attack, said that "After the bomb at Omagh, we were told by Tony Blair and the Taoiseach, Bertie Ahern, that no stone would be left unturned... It seems to me that a lot of stones have been left unturned" but then expressed doubt that the bombing could have been prevented. Lawrence Rush, whose wife also died in attack, said that "There's no reason why Omagh should have happened - the police have been in dereliction of their duty." Other Omagh residents said that the police did all they could. The Belfast Telegraph called the report a "watershed in police accountability" and stated that it "broke the taboo around official criticism of police in Northern Ireland". Upon leaving office on 5 November 2007, Nuala O'Loan stated that the report was not a personal battle between herself and Flanagan and did not lead to one. She also stated that the "recommendations which we made were complied with".
On 19 October 2003, a transcript was released of a conversation between an informer who stole cars on behalf of the RIRA, Paddy Dixon, and his police handler, John White, recorded shortly before Dixon fled the Republic of Ireland on 10 January 2002. Dixon says in the transcript that "Omagh is going to blow up in their faces". On 21 February 2004, PSNI Chief Constable Hugh Orde called for the Republic of Ireland to hand over Dixon. In March 2006, Chief Constable Orde stated that "security services did not withhold intelligence that was relevant or would have progressed the Omagh inquiry." He also stated that the dissident Republican militants investigated by MI5 were members of a different cell than the perpetrators of the Omagh bombing.
In April 2000, the group argued that the attack breached Article 57 of the Geneva Convention and stated that they will pursue the alleged bombers using international law. Michael Gallagher told BBC Radio Ulster that "The republican movement refused to co-operate and those people hold the key to solving this mystery. Because they have difficulty in working with the RUC and Gardai, we can't get justice". In January 2002, Gallagher told BBC News that "There is such a deeply-held sense of frustration and depression" and called the anti-terrorist legislation passed in the wake of the Omagh bombing "ineffective". He has expressed support for the controversial Panorama programme, stating that it reminds "people that what happened in Omagh is still capable of happening in other towns". In February 2002, Prime Minister Tony Blair declined a written request by the group to meet with him at Downing Street. Group members accused the Prime Minister of ignoring concerns about the police's handling of the bombing investigation. A Downing Street spokesman stated that "The Prime Minister of course understands the relatives' concerns, but [he] believes that a meeting with the Minister of State at the Northern Ireland Office is the right place to air their concerns at this stage."
The death of Michael Gallagher's son along with his and other families' experiences in the Omagh Support and Self Help Group form the story of the Channel 4 television film Omagh. Filmmaker Paul Greengrass has stated that "the families of the Omagh Support and Self Help Group have been in the public eye throughout the last five years, pursuing a legal campaign, shortly to come before the courts, with far reaching implications for all of us and it feels the right moment for them to be heard, to bring their story to a wider audience so we can all understand the journey they have made." In promotion for the film, Channel 4 stated that the group has pursued "a patient, determined, indomitable campaign to bring those responsible for the bomb to justice, and to hold to account politicians and police on both sides of the border who promised so much in the immediate aftermath of the atrocity but who in the families' eyes have delivered all too little."
Another song inspired by the bombings was "Peace on Earth" by rock group U2. It includes the line "They're reading names out over the radio. All the folks the rest of us won't get to know. Sean and Julia, Gareth, Ann, and Breda." The five names mentioned are five of the victims from this attack. Another Line, "She never got to say goodbye, To see the colour in his eyes, now he's in the dirt", was about how James Barker, a victim, was remembered by his mother Donna Maria Barker in an article in the Irish Times after the bombing in Omagh. The Edge has described the song as "the most bitter song U2 has ever written". Also, U2 has recited the names of all 29 people killed during the bombing during public performances of their anti-violence anthem "Sunday Bloody Sunday".
Since space for a monument on Market Street itself is limited, the final memorial will be split between the actual bombing site and the temporary Memorial Garden spaced about 300 metres away. Artist Sean Hillen and architect Desmond Fitzgerald won the contest with a design that, in the words of The Irish Times, "centres on that most primal yet mobile of elements: light". A heliostatic mirror will be placed in the memorial park tracking the sun in order to project a constant beam of sunlight onto 31 small mirrors, each etched with the name of a victim. All the mirrors will then bounce the light onto a heart-shaped crystal within an obelisk pillar that stands at the bomb site.
In September 2007, the Omagh Council's proposed wording on a memorial plaque — "dissident republican car bomb" — brought it into conflict with several of the victims' families. Michael Gallagher has stated that "there can be no ambiguity over what happened on 15 August 1998, and no dancing around words can distract from the truth." The Council has appointed an independent mediator in an attempt to reach an agreement with those families. Construction started on the memorial on 27 July 2008.
On 15 August 2008, a memorial service was held in Omagh. Senior government representatives from Britain, Ireland and the Stormont Assembly were present, along with relatives of many of the victims. However, a number of bereaved families boycotted the service and held their own service the following Sunday.