“We knew it would be almost impossible to get an acquittal when a jury hears you confess,” Mr. Peruto said.

Mr. Weintraub said prosecutors learned that Mr. Kratz was hoping to be sentenced to death so that he could become notorious.

“I hope I get the death penalty,” Mr. Weintraub said he heard Mr. Kratz say on prison phone calls, “because then I’ll get the federal defenders and then I’ll be notorious and people will know who I am and I’ll go in a blaze of glory and I’ll never be put to death anyway.”

“Now he doesn’t get to be notorious,” Mr. Weintraub added.

Mr. Kratz’s cousin, Cosmo DiNardo, lured the victims to a farm owned by the DiNardo family in Solebury, Pa., for a supposed drug deal, the authorities said. After four young men from the same area were reported missing, one by one, the investigation transfixed the Philadelphia region.

The authorities discovered that Mr. Finocchiaro’s cellular phone had last had service in the area near Mr. DiNardo’s family farm. The bodies of four victims were found on the farm after an extensive search. They had been partially burned in a roaster made out of an oil drum, and had been buried in a 12-foot-deep hole .

The police already had Mr. DiNardo in custody for lesser charges when they found the bodies. Soon after, Mr. DiNardo confessed to the murders and told investigators that his cousin, Mr. Kratz, had been his accomplice in three of the killings.

The authorities said that Mr. Kratz confessed to shooting Mr. Finocchiaro in the head.

The Finocchiaro family filed a wrongful-death lawsuit against the DiNardo family in 2017, according to their lawyer Tom Kline. They wanted to hold Mr. DiNardo’s family accountable for “negligently providing the weapon” that Mr. Kratz used to shoot their son, Mr. Kline said Monday.