He faced a long list of charges, including enterprise corruption, body stealing, grand larceny, and forgery.
The plea comes more than two years after the gruesome scandal broke, with evidence that corpses were being hacked up without permission or proper screening for diseases and sold for dental implants, knee and hip replacements and other procedures around the country. The looted bodies included that of "Masterpiece Theatre" host Alistair Cooke.
Authorities released photos of exhumed corpses that were boned below the waist. Prosecutors said the defendants had made a crude attempt to cover their tracks by sewing PVC pipe back into the bodies in time for open-casket wakes.
Dressed in a button-down Ralph Lauren shirt and blue jeans, Mastromarino methodically outlined the gruesome scheme in a nearly hourlong confession.
He talked about how he forged records, including the times of death and the ages of the dead, while also telling the judge that he switched blood and tissue samples.
"What he did was wrong," said his defense lawyer, Mario Galluci. "I feel horrible for the victims in this case. There is no excuse for what he did."
The prosecutor said Mastromarino "mutilated the bodies for greed."
Mastromarino was the owner of Biomedical Tissue Services, a New Jersey company that shipped bones, skin and tendons to tissue processors such as Regeneration Technologies Inc., LifeCell Corp. and Tutogen Medical Inc. About 10,000 people received tissue supplied by BTS.
Those companies face hundreds of civil lawsuits from people who received the tissue in transplants and from the families of loved ones who had their body parts taken without permission.
Mastromarino reached the plea deal earlier this year, but it nearly fell apart as prosecutors decided they wanted a trial. A judge nixed that plan, however.