On Wednesday, Lerner sentenced Massof to six to 12 years in prison. The judge credited Massof's decision to plea guilty to two counts of third-degree murder and testify against Gosnell, but called what happened at the clinic "unspeakably horrible."
"As evil as Dr. Gosnell was, as charismatic as he may have been, he didn't do this alone," Lerner said. "He couldn't do this without the assistance of someone like you."
"I don't know how it started," Massof, 51, voice cracking, told the judge.
"I realize that this is something that's wrong and will never be right and will never go away," Massof said, calling his work with Gosnell "a horrific part of my life."
Assistant District Attorney Edward Cameron, who handled the case with Joanne Pescatore, argued for a prison term of 10 to 20 years.
Despite his cooperation, Cameron said, Massof had the education, intelligence, and training to know what he was doing was wrong - and stop it.
Massof, of Pittsburgh, began working at Gosnell's clinic in 2003 and said he quit in 2008, exhausted by the workload, dismayed by deteriorating clinic conditions, and in a dispute with a coworker.
Massof was one of nine Gosnell workers charged in 2011 involving illegal late-term abortions performed at 3801 Lancaster Ave.
Like Gosnell, Massof was charged with first-degree murder for killing infants born live and viable during abortions. He would have faced a possible death sentence if the jury had found him guilty. He pleaded guilty to two counts of third-degree murder in exchange for his cooperation with prosecutors.
In May, a Philadelphia jury found Gosnell guilty of three counts of first-degree murder for killing babies born alive during abortions by snipping their spinal cords with scissors. Gosnell, 72, waived his right to appeal to escape a possible death sentence and is serving three consecutive life terms.
Three more Gosnell workers await sentencing.
Defense attorneys Jeffrey M. Lindy and Paul M. George argued that Massof deserved leniency because of his cooperation and the personal price he had paid.
Lindy said Gosnell had told other inmates Massof was a snitch. Massof has since been threatened and is housed in isolation.
Lindy tried to minimize Massof's participation in abortions, saying he mostly worked upstairs in the clinic's family practice.
Pescatore, however, recounted Massof's trial testimony, in which he said there were so many abortions at the clinic, "I felt like a fireman in hell."
"That's how many babies were falling out," the prosecutor added.