▶ Watch Video: Sneak peek: The Strange Death of Professor Shockley

On the evening of May 11, 2019, three friends gathered around a pool and a hot tub to enjoy a few drinks and play music. By morning, only one was alive.

The sole survivor was Marcus Lillard. First responders had been told that Lillard’s girlfriend, Marianne Shockley, had drowned in the hot tub but sheriff deputies felt something was off about that story. For one thing, Marianne, a respected professor at the University of Georgia, had a bloody gash on her head.

And while deputies were trying to make sense of the scene, the third person at the get-together — homeowner Clark Heindel, a former psychologist — killed himself. He left a three-page suicide note but did not take responsibility for Marianne’s death.

“The devil was at work. I mean, everything that he could have possibly done to line this thing up to make it confusing and deceitful and it was all there,” Marcus Lillard says about that night.

From left, Marcus Lillard, Clark Heindel and Marianne Shockley.

Marcus Lillard/Clark Heindel, Facebook/Marcus Lillard

Lillard tells CBS News correspondent Jonathan Vigliotti, on assignment for “48 Hours,” what he remembers about the bizarre events that night in “The Strange Death of Professor Shockley” airing Saturday, October 15, 2022 at 10/9c on CBS and streaming on Paramount+

Vigliotti and “48 Hours” investigate the complex case that began on the night of May 11 and slipped into the early morning hours of Mother’s Day, May 12, 2019.

That Saturday night, Lillard had brought Marianne to visit their friend Clark Heindel at his home in Milledgeville, Georgia, about 100 miles southeast of Atlanta. It is the town where Southern Gothic novelist Flannery O’Connor wrote her most well-known stories, including “A Good Man Is Hard to Find.” 

Lillard tells Vigliotti there are gaps in his memory from that night because he had been drinking that day and had taken the illegal drug ecstasy that night (also known as MDMA or Molly) along with Marianne and Heindel.

“There is good and there is evil and that night, evil came to play,” Lillard said in the interview. “God has spent the rest of the time cleaning up this mess, and … there’s still some more.” 

He insists Marianne’s death was an accident.

“When I think of an accident,” Vigliotti said to Lillard, “I don’t think of evil. Evil, to me, is intentional.”

Lillard responded, “the Bible says the devil came to steal, kill, and destroy.”

University of Georgia Professor Marianne Shockley took Marcus Lillard along as her assistant on international trips in China and Ecuador. Here they are pictured at the 2nd International Conference “Insects to Feed the World” (IFW 2018) in Wuhan, China.

Marianne, known by her nickname “Doc Shock” to her loyal students, was a specialist in the fields of entomology, the study of insects, and entomophagy, the eating of insects.

Lillard made his living financing cars for a local dealership. He says he and Marianne had been seeing each other on and off for about two years. “We were super in love with each other,” he said.

Heindel was 69 years old — nearly 30 years older than the couple — and told deputies that night that he never got into the hot tub but stayed in the shallow end of pool, about 50 feet away.

No sooner was Marianne in the hot tub than Lillard says he decided to walk into the adjacent woods.  Marianne, he says, begged him not to leave her side.

Marcus Lillard says he doesn’t know how long Marianne Shockley was in the hot tub before he returned to find her lifeless body face down in the water.

Georgia Bureau of Investigation

He told Vigliotti that she said, “Baby … get back in this water with me right now.”

“Was she afraid?” Vigliotti asked Lillard.

“She had fear in her voice and it was … definitely fear,” he replied.

“Why in that moment did you not turn around?” Vigliotti asked.

Lillard was blunt: “Because I’m an idiot.”

He says he is unsure what Marianne was afraid of or how long he was in the woods but that, when he returned, “I could see Marianne slumped down with her chin up to her nose under water …” Investigators believe the men waited up to two hours before 911 was called. 

Longtime Baldwin County Sheriff Bill Massee said it was one of the strangest crime scenes he’d ever come upon.

Lillard agrees that there was something off about that night. “One thing I know for sure,” he told Vigliotti, “is that was no normal ecstasy … it was super potent … and I believe was made with evil hands.”

“What makes you think that ecstasy was evil?” Vigliotti asked.

“Well, it killed two people …” he answered.  

Authorities pegged both Lillard and Heindel as suspects but eventually focused on Lillard. The medical examiner had ruled that Marianne had been strangled. Lillard denied he had caused any harm to Marianne, but he was indicted for felony murder and other charges. After a one-week trial, he was acquitted.