PHILADELPHIA (AP) — A Philadelphia abortion doctor was found guilty Monday of first-degree murder and could face execution in the deaths of three babies who authorities say were delivered alive and then killed with scissors at his grimy clinic, in a case that became a flashpoint in the nation's debate over abortion.

Dr. Kermit Gosnell, 72, was also found guilty of involuntary manslaughter in the drug-overdose death of a patient who had undergone an abortion. He was cleared in the death of a fourth baby, who prosecutors say let out a soft whimper before he snipped its neck.

Gosnell appeared hopeful before the verdict was read and calm afterward; jurors and lawyers on both sides were more emotional.

The jury will return May 21 to hear evidence on whether Gosnell should get the death penalty.

Former clinic employees testified that Gosnell routinely performed illegal late-term abortions past Pennsylvania's 24-week limit, that he delivered babies who were still moving, whimpering or breathing, and that he and his assistants "snipped" the newborns' spines, as he referred to it.

"Are you human?" prosecutor Ed Cameron snarled during closing arguments as Gosnell sat calmly at the defense table. "To med these women up and stick knives in the backs of babies?"

The grisly details came out more than two years ago during an investigation of prescription drug trafficking at Gosnell's clinic in an impoverished section of West Philadelphia.

Authorities said the clinic was a foul-smelling "house of horrors" with bags and bottles of stored fetuses, including jars of severed feet, along with bloodstained furniture, dirty medical instruments, and cats roaming the premises.

Pennsylvania authorities had failed to conduct routine inspections of all of its abortion clinics for 15 years by the time Gosnell's facility was raided and closed down. In the scandal's aftermath, two top state health department officials were fired, and Pennsylvania imposed tougher rules for clinics.

"We see this as triumph of justice," said Charmaine Yoest, president and CEO of Americans United for Life, a group that has taken a lead role in efforts to enact anti-abortion laws in state legislatures.

Four former clinic employees have pleaded guilty to murder and four more to other charges. They include Gosnell's wife, Pearl, a cosmetologist who helped perform abortions.

Both sides of the abortion divide seized on the case. Abortion foes said it exposed the true nature of abortion in all its disturbing detail. Abortion rights activists warned that Gosnell's rogue practice foreshadows what poor and desperate young women could face if abortion is driven underground with more restrictive laws.

Midway through the six-week trial, anti-abortion activists accused the mainstream media of ignoring the case because it reflected badly on the abortion rights cause. Major news organizations denied the allegation, though a number promptly sent reporters to cover the trial.

After prosecutors rested their case, Common Pleas Judge Jeffrey Minehart threw out for lack of evidence three of seven murder counts involving aborted fetuses. That left the jury to weigh charges involving fetuses identified as Baby A, Baby C, Baby D and Baby E.

Prosecution experts said one was nearly 30 weeks along when it was aborted, and it was so big that Gosnell allegedly joked it could "walk to the bus." A second fetus was said to be alive for some 20 minutes before a clinic worker snipped its neck. A third was born in a toilet and was moving before another clinic employee grabbed it and severed its spinal cord, according to testimony.

Baby E let out a soft whimper before Gosnell cut its neck, prosecutors alleged. Gosnell was acquitted in that baby's death, the only one of the four in which no eyewitness account was given during the trial.

Gosnell's attorney, Jack McMahon, argued that none of the fetuses was born alive and that any movements were posthumous twitching or spasms.

He also contended that the 2009 death of 41-year-old Karnamaya Mongar of Woodbridge, Va., a Bhutanese immigrant who had been given repeated doses of Demerol and other powerful drugs to sedate her and induce labor, was caused by unforeseen complications.

Gosnell was also convicted of infanticide, racketeering and more than 200 counts of violating Pennsylvania's abortion laws by performing third-term abortions or failing to counsel women 24 hours in advance.

Gosnell did not testify, and his lawyer called no witnesses in his defense. But McMahon argued that the doctor provided desperate young woman with "a solution to their problems," and he branded prosecutors "elitist" and "racist" for pursuing his client, who is black and whose patients were mostly poor minorities.

"We know why he was targeted," McMahon said.

Prosecutors described Gosnell's employees as nearly as desperate as the patients. Some had little or no medical training, and at least one was a teenager still in high school. One woman needed the work to support her children after her husband's murder.

Stephen Massof, an unlicensed medical school graduate who could not find a residency, told jurors that Gosnell taught him how to snip babies' spines, something he then did at least 100 times at the clinic.

"I felt like a fireman in hell," Massof testified. "I couldn't put out all the fires."

Gosnell still faces federal drug charges. Authorities said that he ranked third in the state for OxyContin prescriptions and that he left blank prescription pads at his office and let staff members make them out to cash-paying patients.

He performed thousands of abortions over a 30-year career. Authorities said the medical practice alone netted him about $1.8 million a year, much of it in cash. Authorities found $250,000 hidden in a bedroom when they searched his house. Gosnell also owned a beach home and several rental properties.

"He created an assembly line with no regard for these women whatsoever," Cameron said. "And he made money doing that."