The admitted triple murderer, Gary Lee Sampson, 57, could be the second person sentenced to death by a federal jury in Massachusetts in two years, a rarity in a state whose laws do not allow the death penalty.
Sampson pleaded guilty to murdering two men who picked him up while he was hitchhiking in Massachusetts and a third man in New Hampshire.
Assistant US Attorney Zachary Hafer showed the jury the pocketknife that Sampson used to stab two of his victims to death, as well as photos of his victims before and after their slayings.
"Three kind, caring souls, seemingly unconnected to each other in any way but brought together in the most unimaginably tragic way, brought together by the pure heinousness and cruelty of that man," Hafer said, pointing to Sampson.
This is the second trial to determine if Sampson will be executed. He was sentenced to death in 2004, but a judge in 2011 overturned that sentence after learning that one of the jurors had lied about her history as a victim of domestic violence.
That decision set the stage for a second sentencing trial, which has played out over the past two months. Lawyers for Sampson, who will make their closing arguments later on Wednesday, argued that the jury should spare his life due to a history of being the victim of abuse as a child, mental illness and drug abuse.
Sampson himself addressed the court last month, apologizing for killing two men, aged 69 and 19, in Massachusetts, then murdering the 58-year-old caretaker of a vacation home he broke into in neighboring New Hampshire.
If the jury decides not to sentence Sampson to death, he will spend the rest of his life in federal prison.
Sampson's victims were Philip McCloskey, 69, Jonathan Rizzo, 19, slain in Massachusetts, and Robert Whitney, 58, killed in New Hampshire.
Hafer noted that Sampson strangled Whitney to death rather than stabbing him. Hafer said Sampson later told investigators, "Why was Whitney choked to death? Because Sampson was sick of getting blood on himself."
Gary Lee Sampson
A US prosecutor on Wednesday recounted in brutal detail how a Massachusetts man slaughtered three men, including two who had picked him up hitchhiking, in 2001 as he sought to persuade a jury to sentence the confessed killer to die.
