On Wednesday, Gosnell, 69, was charged with murder in the deaths of Mongar and seven babies who prosecutors say were delivered, alive, in the final months of pregnancy.
A grand jury report found that Gosnell had severed the spinal cords of those babies, operated without licensed caregivers, spread disease with infected instruments, and perforated patients' wombs and bowels.
A once-respected activist, Gosnell now sits in prison without bail. Nine of his employees have been charged with offenses, including four with murder.
Gosnell has professed his innocence in the past.
Since his arrest, a portrait has emerged of a bright young man who was brought in to help rebuild Mantua but ultimately may have done far more to bring it down.
Over the years, his abortion practice deteriorated. He prescribed drugs freely, investigators say. And in the twilight of his career, he has become a symbol for those who would tighten restrictions on all abortion providers.
Gosnell grew up an only child in West Philadelphia and attended prestigious Central High School. After graduating from Jefferson Medical College in 1966, he moved briefly to New York City to work at an abortion clinic, learning early-term techniques in the days before the U.S. Supreme Court's Roe v. Wade decision formally legalized the procedure.
Mantua was a hotbed of gang and drug activity, and a group of organizers, called the Young Great Society, was trying to change that. The neighborhood had no doctor, and the group asked Gosnell to open an office there, said Walter Edmonds, a childhood friend.
As boys, the two had worked together at a grocery at 52d and Market Streets. Edmonds later helped Gosnell open a methadone clinic on 38th Street called the Mantua Halfway House, as well as an abortion clinic on 36th Street. Both were rare in the city.
"It was very exciting, let me tell you," said Edmonds, 70. "It was very pioneering."
Gosnell, he recalled, "was very dynamic, charming, and he had an inclination to make some money."
Sidney H. Schnoll recalled being recruited by Gosnell to volunteer at the drug clinic when both were medical residents at Jefferson in the late 1960s.
"He said he came from that community," said Schnoll, now a national expert on addiction and pain management. "He wanted to give back to the community, which I thought was a terrific thing."
By the early 1970s, Gosnell had married his first wife, a nurse, and had two children. One is a doctor in California, the other a French professor at an elite women's college. Gosnell would go on to divorce and marry twice more.
He also became known among activists for his willingness to take risks that others wouldn't.
In 1972, he played a prominent role in a scandal over an experimental abortion tool called "the super coil," designed for use in the second trimester.
California psychologist and activist Harvey Karman had developed the coil. Gosnell tested it on 15 poor women who had taken a bus from Chicago on Mother's Day weekend because they couldn't get abortions elsewhere.
Federal and city health officials later found that nine of the women had suffered serious complications, including a punctured uterus. One needed a hysterectomy.
Gosnell was not charged, but Karman spent two years in court battles with Philadelphia District Attorney Arlen Specter before getting cleared.
In his early years, Gosnell had a good reputation in part because he made house calls.
But he was also known for pushing the limits. His methadone clinic once employed 25 people, Edmonds said, before it unraveled.
State tax liens piled up against the clinic through the 1980s and 1990s, and it folded.
Gosnell also became more reckless in his abortion practice, which was hit by a $41,000 federal tax lien.
He couldn't get doctors to refer patients because of his declining reputation. So he increasingly relied on attracting women from out of state. He even provided a bed in the clinic for overnight stays, the grand jury report said.
Gosnell also accepted women who couldn't get abortions elsewhere. He treated patients who had complications or were too far along in their pregnancy for reputable doctors to treat.
Yet his recent downfall started for another reason: his alleged penchant for prescribing painkillers such as Percocet. Federal drug agents raided his clinic, now at 38th Street and Lancaster Avenue, on Feb. 18.
That raid triggered another inspection by health investigators four days later. They found his clinic was filthy, with fetal remains filling a freezer and clogging drains. He allowed unlicensed employees to give anesthesia, often leaving patients unattended, the report said.
And he once said he had killed a six-pound baby who "could walk me to the bus stop," an employee told authorities.
His employees were largely complicit or clueless, or both, the grand jury report found.
One of the few former employees who filed a detailed complaint, in 2001 with the Pennsylvania Department of State, got nowhere - which was typical.
Indeed, state regulators - and to a lesser extent those in the city - repeatedly failed to stop Gosnell.
The Pennsylvania Department of Health opted not to investigate complaints, including the death of Mongar, according to the grand jury's report.
"People die," Christine Dutton, the department's chief counsel, told the grand jury, arguing there was no reason to think Mongar's death was suspicious.
Between 2002 and 2009, the grand jury learned, attorneys for the state's medical licensing board reviewed five cases against Gosnell.
They closed three without investigation. The last two were investigated and closed without action - including the death of a 22-year-old whose family sued Gosnell and received a $400,000 settlement.
Edmonds, who ran Gosnell's methadone clinic but left on bad terms, said he was dismayed by the news about Gosnell, but not entirely surprised - even by the detail that Gosnell kept the feet of fetuses in jars.
"It sounded like him," he said. Gosnell "always operated outside of the norm. Wherever the boundary was, he just sort of reached beyond."
From the Grand Jury
Here are selections from the grand jury's 260-page report, which last week led to criminal charges against family physician Kermit Gosnell and nine employees:
Gosnell regularly delivered live babies in the third trimester of pregnancy, then murdered them by what he called "snipping," severing their spinal cords with scissors. "It was a baby charnel house," referring to a vault for storing human remains, the report said.
None of the clinic employees had medical licenses, yet they administered drugs and performed procedures, including "snipping."
The three-story facility at 3801 Lancaster Ave. was a maze of filthy rooms and narrow hallways. It lacked basic medical equipment and emergency access for stretchers.
Gosnell, who showed up to do abortions at night, left blank, presigned prescription pads so patients of his first-floor "pain management clinic" could get Oxycontin and other narcotic painkillers during business hours.
For two decades, state authorities and, to a lesser degree, city health officials ignored complaints and red flags. The grand jury concluded this inaction was "because the women in question were poor and of color, because the victims were infants without identities, and because the subject was the political football of abortion."
Contact staff writer Chelsea Conaboy at 215-854-4193 or email@example.com.
Inquirer staff writers Vernon Clark, Marie McCullough, and Don Sapatkin contributed to this article.