How Police Tracked Down a Serial Killer Who Got Away with It for Years by Preying on the Elderly

Mary Bartel, 91, was an early riser.  

On the morning of March 19, 2018, the feisty grandmother woke up at 4:30 a.m., took her blood pressure and then went for her daily walk around the grounds of the Preston Place Retirement Community in Plano, Texas.

She then drove to a 6:30 a.m. church mass before returning to her first-floor apartment she’d once shared with her husband before he passed away.

Bartel was at her computer writing an email when she heard someone incessantly knocking on her door.

“I opened the door and I saw this man with his green rubber gloves on,” she later told authorities. “I tried to push back but I’m 91-years-old and he is young and muscular. And he just said, ‘Don’t fight me. Just get on the bed.’”

Fearful, Bartel complied.

The man then grabbed a pillow and attempted to smother her — and the horrific story is the subject of the upcoming episode of People Magazine Investigates. Titled “A Serial Killer’s Playbook,” the episode premieres Monday, November 25 at 9/8c on ID. (An exclusive clip is shown below.)

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“I felt as though I could not breathe,” she said. “I thought I would die. I am not afraid to die but I didn’t want to die that way.”

Convinced that Bartel was dead, the man stole some jewelry before fleeing the retirement complex.

When Bartel didn’t show up to her exercise class, a friend stopped by to check on her and found her unconscious, but still breathing.

As she was transported to the hospital, she regained consciousness and told authorities about her brutal ordeal.

Ultimately, the attack on Bartel changed everything for law enforcement.

Before the attempted murder of Bartel, more than six women died at the same retirement complex, but police assumed they’d died from natural causes.

The same day of Bartel’s attack, police learned of another suspicious death. Ann Conklin, 82, who lived in the apartment across the hall from Bartel, was found dead in her apartment by her daughter. Her ring and watch were missing.

Police canvassed the complex and learned that the son of a resident reported a stranger loitering in the parking lot a few days earlier.

The witness had written down a license plate for the stranger’s Nissan Altima.

Investigators ran the license plate number and discovered the vehicle was registered to Billy Chemirmir, a former health care worker who’d moved to the United States in 2003 from Kenya.

The following day, on March 20, Chemirmir was arrested in the parking lot of his Dallas apartment complex after authorities watched him toss into the dumpster a distinct red wooden jewelry box with Asian markings.  

Legal papers found in the jewelry box tied him to the murder of 81-year-old Lu Thi Harris, who was found smothered to death with a pillow in her bedroom.

In total, Chemirmir was charged with the murders of 22 seniors between 2016 and 2018.

Authorities alleged that Chemirmir targeted elderly people living in upscale senior living facilities. He would allegedly dress as a maintenance worker or health care aide and kill his victims before robbing them. Because the victims were between 76 and 94, their deaths weren’t investigated thoroughly, with most people believing they’d died of natural causes.

He was convicted of killing two elderly women, including Harris, NBC5 reported.

Chemirmir, 50, was found murdered in his Texas prison cell by his cellmate in September 2023, per the Associated Press.

People Magazine Investigates: A Serial Killer’s Playbook premieres Monday, November 25 at 9/8c on ID.