When he was 13, he stabbed a young girl with a pencil and felt sexually stimulated when she cried in pain. The next day, he took a razor blade and slashed another girl as he biked past her. He was never caught for either attack. In another incident, he beat and nearly strangled another boy. He relished the power of bullying, and began to stab or slash others.
Danny Joe Eberlee disappeared while delivering the Omaha World-Herald newspaper on Sunday, September 18, 1983, in Bellevue, Nebraska. His brother, who also delivered the newspaper, had not seen him, but did remember being followed by a white man in a tan car on previous days. It was found that Eberle had only delivered three of the 70 newspapers on his route. At his fourth delivery, his bicycle was discovered along with the rest of the newspapers. There appeared to be no sign of a struggle. Joubert would later describe how he had approached Eberle, drew a knife and then covered the boy's mouth with his hand. He then instructed the boy to follow him and took him to his truck. He then took him to a gravel road outside of town.
After three days of searching, his body was finally discovered about four miles (6 km) from where his bike was found. He had been stripped to his underwear, had his feet and hands bound and mouth taped with surgical tape. Joubert had stabbed him nine times. As a kidnapping, the crime came under the jurisdiction of the federal government of the United States, so the FBI was called in.
The investigation followed several leads, including a young man who was arrested for molesting two young boys about a week after the crime. He failed a polygraph test and had a false alibi but did not fit the profile the FBI had created for the murderer. He was released due to a lack of evidence. Other known pedophiles in the area were also questioned, but the case went cold due to a sparcity of evidence.
On December 2, Christopher Walden disappeared in Papillion, Nebraska, about three miles (five km) from where Eberle's body was found. Witnesses again said they saw a white man in a tan car. Joubert said that he had driven up to Walden as he walked, showed him the sheath of his knife and ordered him into the car. After driving to some railways lines out of town, he ordered Walden to strip to his underwear which he did. But then Walden refused to lie down. After a brief struggle, Joubert overpowered and then stabbed him. Joubert cut Walden's throat, so deep that he had almost been decapitated. Walden's body was found two days later five miles (eight km) from the town. Although the crimes were similar there were differences. Walden had not been bound, had been concealed better, and was thought to have been killed immediately after being abducted.
A search warrant was issued, and rope consistent with that used to bind Danny Joe Eberle was found in his dorm room. The FBI found that the unusual rope had been made for the United States military in South Korea. Under interrogation, Joubert admitted getting it from the scoutmaster in the troop he was an assistant in.
In 1995, Joubert filed a writ of habeas corpus to the United States federal courts over the death sentences. His lawyers argued that the aggravating factor of "exceptional depravity" was unconstitutionally vague. The court agreed and the state of Nebraska appealed to the United States District Court for the District of Nebraska. They overturned the appeal, saying that he had shown sadistic behavior by torturing Eberle and Walden.
As part of appeals on the Nebraska Supreme Court over whether the electric chair in Nebraska is a cruel and unusual punishment, it was revealed that during his execution Joubert incurred a four-inch brain blister on the top of his head and blistering on both sides of his head above his ears.