Greg McDonald is not squeamish about dead bodies.

Now dean of health sciences at the Philadelphia College of Osteopathic Medicine, McDonald previously served as Philly’s assistant medical examiner, where his job was helping determine the cause of sudden deaths across the city.

For nearly a decade and a half, McDonald was an integral part of the office’s day-to-day functions.

He knew an investigative position would be a good fit back when he was at PCOM for medical school. As he learned the skills necessary to treat sick people, he saw that wasn’t really his passion. McDonald would prefer to explore mysteries, he realized — to examine tissue, to poke and prod at human bodies whose life had been stolen, so he and others could understand why they died.

“It’s sobering work,” McDonald told Billy Penn. “We never get to speak to happy families. But you have to take your victories in different ways.”

A victory in this field? Accurately identifying cause of death. That can help restore justice, McDonald said, and it can ease the healing process for loved ones.

Over the years, the corpse connoisseur has seen some pretty spooky stuff. McDonald has helped identify plenty of murderers — even serial killers — in Philadelphia, all the while observing their impact on the field of medical examination.

Below are four gripping and sometimes gruesome examples, which McDonald says changed the industry forever.

[Editor’s note: This story has descriptions of true crime, which can be somewhat graphic and intense. If you are easily disturbed by things of this sort, continue at your own risk.]

The woman who killed all her children

McDonald started working in Philly just in time to see Marie Noe apprehended.

The Kensington woman’s life was long viewed as a series of sad misfortunes. From 1949 to 1968, Noe watched all 10 of her children die — the cause for eight of them believed to be sudden infant death syndrome. The other two were lost to complications at birth.

So many of Noe’s children died, McDonald said, that city medical examiners started to wonder whether there was some sort of genetic issue present in the family.

In 1963, Life magazine published a sympathetic article about the tragic situation using the pseudonym Martha Moore. Noe continued to fly under the radar, living in her Kensington home for decades.

But in the late 1990s, a New York woman was found to have killed all five of her children — and their deaths had been initially misidentified as sudden infant death syndrome.

That realization sparked new interest in Noe’s situation. The Philadelphia Police Department reopened the case and eventually got her to confess to smothering four of her children to death. She claimed she couldn’t remember what happened to the others.

This used to happen often, McDonald said. Smothering doesn’t usually present any obvious signs on a dead body, he clarified, especially if it’s a child. And for a long time, when investigating a young death, if a medical examiner couldn’t find anything suspicious, they’d just label it SIDS and classify it as a “natural” cause.

“[Noe’s case] changed the way a lot of us look at childhood deaths,” McDonald said. Medical examiners will now often label the cause “undetermined” to leave the door open for future investigation.

McDonald believes the classification could save lives.

“If someone calls it undetermined at the beginning, it sends up a red flag to other investigators who may be involved somewhere else,” McDonald said. “If you say the death was natural, they’ll just go with that. But three or four ‘undetermineds’ makes you wary.”

The man who put women in cages

Gary Heidnik’s reign of terror started in North Philly in 1986.

At his home at 3520 North Marshall St., Heidnik kidnapped eight women and killed two of them. He put them through hell — keeping them locked in cages in his basement, starving them and even torturing them by electrocution.

His first victim, Sandra Lindsay, died due to a combination of starvation and untreated fever. A fact not for the faint of heart: Heidnik disposed of her body by dismembering her and cooking her in the oven, then making her into dog food.

“That certainly was a grisly case,” recalled McDonald, who started in the medical examiner’s office a few years later. “That’s really kind of a different level of torture.”

Police allegedly came to Heidnik’s home due to complaints of a bad odor, but left after hearing Heidnik’s excuse: “I’m cooking a roast. I fell asleep and it burnt.”

Heidnik killed another woman, Deborah Dudley, via relentless electrocution. He disposed of her body in the New Jersey Pine Barrens.

Heidnik was apprehended in 1987, when one of the women he tortured managed to call 911.

McDonald called the case a cautionary tale that proves the need to take prior crimes seriously. Heidnik had been arrested several times: for aggravated assault against his neighbor in the 1976, kidnapping his girlfriend in 1978, then spousal rape in 1986.

“It wasn’t the first time he had done those things,” McDonald said. “With so many of them, there’s something leading up to the ultimate event. They don’t just wake up one day and say, ‘I’m going to do this.’”

The sex assault perpetrator in the heart of the city

Philly residents of the late ’90s came to fear a man known as the Center City rapist.

Troy Graves struck at least five times between 1997 and 1999. His first noted sexual assault attempt was a woman living on South 21st Street. Then he hit three consecutive times at locations along Pine.

In May 1998, Graves raped and murdered Wharton doctoral student Shannon Schieber — his only fatality in Philly. The next year, he sexually assaulted a woman on Naudain Street.

After his handful of heinous crimes in Philadelphia, Graves relocated to Colorado, where he continued hurting women until the early 2000s. He wasn’t apprehended until 2002, after almost a dozen women had suffered at his hand.

To McDonald, Shieber’s death was especially tragic. He recalls that a neighbor reported hearing sounds of a struggle and called the police. Arriving at the scene, they knocked at the door, didn’t hear anything and left.

“He was in the process of strangling her, and they didn’t break down the door,” McDonald said. “That was particularly sad.”

The one known as the Kensington strangler

The so-called “Kensington strangler” struck Philly in 2010.

Dubbed a “sexual serial killer” by the media, Antonio Rodriguez raped and killed three women in just two months: Elaine Goldberg, Nicole Piacentini and Casey Mahoney.

The 22-year-old claimed he just wanted to have rough sex, and that the womens’ deaths by strangulation were an accident. But medical examiners quickly called BS.

“I’ve testified to this a lot,” McDonald said of deaths by strangulation. “Even if you do it really well, the victim still has about 10 seconds of blood in their head and maintain consciousness. Even after they pass out, you have to hold it for a minute or two until they have brain damage, and then three or four minutes until they die.

“So for someone to say, ‘I didn’t mean to do it,’ that doesn’t fly,” he explained.

Still, it can be hard for an examiner to identify a death by strangulation. There’s usually no internal signs, and oftentimes a killer won’t leave a mark on their victim’s neck. The only helpful sign, McDonald said, is if a victim has popped blood vessels in their face and eyes.

“When the neck is being compressed, you’re cutting off the jugular veins first,” he said. “But your arteries are still pumping blood into the brain. There’s an increase in pressure, which results in the rupture of small blood vessels.”

MEO unit supports grieving loved ones

In addition to forensic investigators like McDonald was, Philly’s MEO maintains an entire unit to offer support for loved ones.

The office has social workers on site who can provide free counseling and referral resources. Most often, the services are over the phone — but in cases of child and infant deaths, counselors will visit homes. They can also assist with burial or cremation.