Gosnell, 72, showed no outward emotion as the jury foreman read the verdict in a Common Pleas courtroom filled with dozens of journalists.
Gosnell, a once-respected native son of West Philadelphia, now faces the prospect of the death penalty.
In addition to the four first-degree-murder counts, and one count of third-degree murder for the 2009 drug overdose death of Mongar, Gosnell also stood trial on multiple counts related to performing late-term abortions.
Gosnell also was convicted of 21 of 24 illegal-late-term-abortion charges, and not guilty of three.
In addition, he was found guilty of hundreds of other charges, including:
- Infanticide on Baby A;
- Conspiracy on Babies C and D;
- Running a corrupt organization, a racketeering charge;
- Conspiracy to commit corrupt organizations;
- Conspiracy abortion beyond 24 weeks;
- Conspiracy informed-consent violations.
Gosnell did not testify during the six-week trial, but often smiled affably when entering and exiting the courtroom and when chatting with Jack McMahon, his attorney.
Gosnell and nine employees of his now-closed Women's Medical Society clinic were arrested following a Jan. 19, 2011, grand jury investigation and report that documented rampant wrongdoing inside a facility that the grand jury described as "filthy," "deplorable" and "disgusting."
The grand jury was convened after a Feb. 18, 2010, FBI and police raid triggered by tips that Gosnell also had turned his clinic into a "pill mill" where he made perhaps millions of dollars illegally selling prescriptions for painkillers including Oxycontin.
During the raid, officials found 47 fetuses in bags and plastic drinking bottles in the basement and in freezers, and other evidence of illegal abortions.
McMahon told the trial jury of seven women and five men that Gosnell was not guilty of murdering the four babies because they were born dead as a result of an abortion drug. He called the drug-overdose death of patient Mongar, 41, an accident.
During the trial - which began March 18 with fiery prosecution and defense opening statements - the jury saw a parade of former Gosnell employees and patients who recounted witnessing or participating in the gore and criminality that led prosecutors to dub the clinic a "house of horrors."
They spoke of seeing babies born with chests moving up and down, moving limbs and even, in one case, an alien-like cry.
Of the nine former employees arrested with Gosnell, eight pleaded guilty before the trial started, and six of those defendants testified for the prosecution.
First up was Adrienne Moton, 35, who spent four years in Gosnell's employ helping with abortions despite having only a high school education.
Moton, of Upper Darby, cried when she recalled "Baby A," as the child was called in court. Born in July 2008 to a 17-year-old mother in the 29th week of pregnancy, the baby looked viable, said Moton, who took a picture of the child.
"I just felt he could have had a chance," she said. "He could have been born any day."
Baby A's mother, Shayquana Abrams, 21, of Chester, testified that the abortion she underwent left her hospitalized for two weeks with a blood clot to the heart, a grapefruit-sized abscess and continuing bouts of fatigue, headaches and shortness of breath.
"I never felt pain like that before," the woman said, weeping on the witness stand.
Defendant Steven Massof, an unlicensed medical doctor, testified about "fetuses and blood" littering the abortion clinic where he, Gosnell and other employees routinely snipped the spinal cords of babies born alive.
"It is literally a beheading. It is separating the brain from the body," Massof, 50, of Pittsburgh, testified.
Former clinic employee Kareema Cross, 28, who was not charged in the case, testified that she saw ten babies breathing and five babies moving before being killed.
The former medical assistant said she was so appalled by Gosnell's ghoulish practices and the rundown condition of his clinic that she began taking pictures of the facility and eventually reported him to federal authorities.
Defendant Lynda Williams, 44, of Wilmington, testified that Gosnell told her it was "standard procedure" to cut the necks of babies and he taught her how to do like wise.
"It gave me the creeps," said Williams, who pleaded guilty to two counts of third-degree murder for the deaths of a baby and Mongar.
When a baby moved, she said, Gosnell explained it as an "involuntary movement - last breath."
More details to come.
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