US District Judge Jack Weinstein said he would not formally impose the maximum sentences on Louis Eppolito and Stephen Caracappa until at least June 23, giving the defendants time to argue that they were not adequately represented.
"This is probably the most heinous series of crimes ever tried in this courthouse," the judge said.
The two former partners were convicted by a jury in April of participating in eight slayings between 1986 and 1990 while simultaneously on the payroll of the New York Police Department and the Luchese crime family.
Prosecutors said the detectives committed some of the murders themselves, stopping the victims' vehicles at traffic stops. Other victims were kidnapped before being delivered to the Mafia to be killed.
The court also heard that the pair once arrested a Mafia figure, only to hand him over to be tortured and murdered.
Eppolito, 57, and Caracappa, 64, received US$4,000 (A$5,333) a month from Luchese underboss Anthony "Gaspipe" Casso, who also used them to get inside information on law enforcement investigations.
Their pay went up for the murders: They earned US$65,000 (A$86,672) for one killing.
Federal prosecutor Daniel Wenner had described the case as "the bloodiest, most violent betrayal of the badge this city has ever seen".
Both men had been decorated for their efforts as detectives and retired in the early 1990s. They both denied the allegations.
Eppolito wrote a book about his life in 1992 called Mafia Cop: the Story of an Honest Cop Whose Family Was the Mob,
He also played bit parts in a number of films between 1990 and 2005, including Goodfellas, Mad Dog and Glory and Predator 2, and wrote the screenplay for mobster flick Turn of Faith in 2001.