The Queen was out riding on Constitution Hill with her husband, Prince Albert, on 10 June, when Oxford shot twice at the couple, missing both times. He was seized by onlookers, arrested and tried at the Old Bailey in July 1840. He was acquitted by reason of insanity and sent to Bethlem Royal Hospital, where he remained until the criminal patients of the institution were transferred to Broadmoor Hospital in 1864. Three years later, he was offered a discharge if he would agree to leave the country. He is believed to have lived out the rest of his life in Australia.
At the time of the crime Victoria was pregnant and expecting her first child, so that the public was aware of the real danger the young queen faced from the assassination. Rumors arose about the actual nature of the attack. Oxford (who was a "potboy" in a tavern) probably was mentally ill, but his rooms were searched and there was "evidence" that suggested he was a member of a group who were against the government. This was not too unreal for the public, aware of the threats from chartism supporters, and also of other political radical groups that threatened the government, such as Arthur Thistlewood and his Cato Street Conspiracy group in 1820. But what was most curious was a letter the public called "the Hanover Letter". This proved to be written by Oxford but was supposedly signed by Ernest Augustus I of Hanover and Duke of Cumberland. Victoria's uncle (the fifth son of King George III, was made King of Hanover in 1837 upon the death of William IV of England and Hanover (Hanover had salic law, allowing only male rulers). If Victoria died without any heirs, Ernest would become King Ernest I of Great Britain. As Ernest was an able but reactionary man, he would not have been a popular or successful British monarch. Ernest was also widely regarded as responsible for the murder of a valet in 1810 at Kensington Palace (a matter still in dispute - the valet, De Sellis, may have attacked Ernest and committed suicide). Though eventually discredited, for awhile the Hanover Letter looked like a plot cooked up by an ambitious heir against the Queen.