FILE - Gary Lee Sampson, center, is escorted into Hillsborough County Superior Court, June, 1 2004, in Nashua, N.H. A federal appeals court is considering vacating the murder convictions of Sampson, convicted of killing two Massachusetts men in carjackings in 2001, because he was still appealing his execution when he died in prison last month. The Federal Bureau of Prisons says Sampson, 62, died Tuesday, Dec. 21, 2021. (AP Photo/Jim Cole, File)

BOSTON (AP) — Prosecutors are opposed to vacating the murder convictions of a man who died in prison while appealing his death sentence for brutally killing three men more than 20 years ago in New England, according to a legal brief filed Friday.

U.S. District Attorney for Massachusetts Rachael Rollins’ office said in the brief filed in Boston federal court that Gary Lee Sampson’s Dec. 21 death makes his pending appeal moot but doesn’t call into question his convictions or sentences.

Sampson pleaded guilty to carjacking and killing three men and never challenged those convictions, making them final and no longer open to appeal, the office said.

“This Court should simply dismiss this appeal as moot and leave Sampson’s convictions and sentences undisturbed,” Rollins’ office concluded.

Federal prosecutors and defense lawyers are submitting legal briefs this month as the U.S. First Circuit Court of Appeals considers the legal implications of Sampson’s death.

Rollins’ arguments echoed sentiments earlier this week from one of Sampson’s lawyers.

“No one is challenging Gary’s conviction,” Madeline Cohen said. “Gary Sampson never denied responsibility for killing Jonathan Rizzo, Phillip McCloskey, or Robert Whitney. He pled guilty in 2003 and always stood by that guilty plea.”

In July 2001, Sampson stabbed Rizzo and McCloskey to death after they separately gave him rides in Massachusetts. He then broke into a home in New Hampshire and strangled Whitney to death.

Sampson’s lawyers had argued he was brain damaged and mentally ill during the killing spree.