Williams said Gosnell assured her what she saw was "involuntary movement, a last breath" and that abortion drugs had already doomed the fetus which was in its second trimester of 12 to 24 weeks.
Williams, who pleaded guilty to two counts of third-degree murder to escape a possible death penalty or life in prison, was on the witness stand for almost five hours Tuesday and returns Wednesday to undergo further questioning by defense attorney Jack McMahon.
McMahon focused on the fact that Williams had on-the-job training to work in Gosnell's abortion clinic even though she was not licensed or certified in any of those jobs.
Like most former Gosnell employees, Williams fit a certain mold: low education - she didn't finish eighth grade - and a host of dire personal problems.
Williams testified that she first met Gosnell when she was working as an instrument sterilizer at Atlantic Women's Medical Services clinic in Wilmington, where Gosnell performed abortions on a part-time basis.
Then, in 2007, Williams told the Common Pleas Court jury, her husband was murdered and her life fell apart.
She said she could not meet the required hours for the Wilmington job. Diagnosed with bipolar illness and depression, Williams said she took her three children and moved to Chester and looked for work.
Williams said she called Gosnell and asked if he had openings, and he hired her, under the table, to sterilize instruments.
He also became her personal physician, writing prescriptions for the drugs needed to treat her mental illnesses.
Williams, who said she had training as a phlebotomist, was soon moved by Gosnell into other jobs: ultrasounds, administering intravenous medication and anesthesia to abortion patients.
Williams testified in a flat, emotionless voice and at times seemed catatonic, taking several seconds before reacting to questions.
One of her duties, Williams said, was to retrieve fetuses women would sometimes spontaneously abort in the waiting room after getting large doses of drugs to dilate the cervix.
One day, Williams testified, a woman expelled a second-trimester fetus into the toilet and it was moving. Williams said she took a pair of scissors and snipped the spine as Gosnell showed her.
"I did it once, and I didn't do it again because it gave me the creeps," Williams said.
Williams also told of how she administered the anesthesia on Nov. 19, 2009, the night abortion patient Karnamaya Mongar went into cardiac arrest.
Prosecutors alleged that Mongar, 41, of Virginia, was overdosed with Demerol. That is the basis of one third-degree murder charge that Williams pleaded guilty to and also the third-degree murder charge against Gosnell.
Gosnell, 72, is also charged with seven counts of first-degree murder involving infants born live during illegal late-term abortions and killed with scissors.
McMahon questioned Williams at length about the differing estimates of how much Demerol she gave Mongar in statements to the FBI and Philadelphia homicide detectives and in court.
As Gosnell performed the abortion on Mongar, Williams testified, she watched the pulse in the patient's neck grow fainter and her skin get grayer.
After the procedure was over, she said, Gosnell listened for a heartbeat and found none.
"The doc got freaked out, hysterical," Williams testified. "He started doing CPR immediately."
Paramedics restored a heartbeat but Mongar was brain-dead when she reached the emergency room of the Hospital of the University of Pennsylvania.
Contact Joseph A. Slobodzian at 215-854-2985, firstname.lastname@example.org, or @joeslobo on Twitter.
Inquirer staff writer Sulaiman Abdur-Rahman contributed to this article.