How a small piece of a bathroom door lock helped solve the murder of a Minnesota nurse

In the morning of December 16, 2022, St. Paul, Minnesota, homicide detectives Abby DeSanto and Jennifer O’Donnell are called to a downtown apartment building to investigate a reported suicide. A 32-year-old woman named Alexandra Pennig was found dead in the bathroom with a gunshot wound to the head.

For detectives, what really happened to Pennig is something that still haunts them to this day. And that’s the question at the center of “The Strange Shooting of Alex Pennig,” reported by “48 Hours” contributor Natalie Morales airing Friday, October 26 at 10/9c on CBS and streaming on Paramount +.

When detectives DeSanto and O’Donnell arrive at the apartment, they learn that Pennig was not alone when she died. A man named Matthew Ecker was also there. Ecker and Pennig were nurses and had met two years earlier when they worked at the same clinic. Ecker told the first responders the gun, and that Pennig had grabbed, locked in the bathroom, and then fired shot. “I thought everything was fine,” he said. “And he just held a gun.” Ecker told first responders that after hearing the shots, he immediately opened the bathroom door: “I tried to do what I could. Then I washed my hands … That’s why I didn’t have anything on my hands.” Ecker said he then called 911. But it was too late. He said he didn’t understand why Pennig would do this.

In Pennig’s apartment, there was alcohol and six bottles of prescription drugs, including an antidepressant, all given to Pennig. To the detectives, it was suggested that Alex might be depressed, and they wondered if Ecker’s story that he killed himself was true.

But he also remembers someone disputing Ecker’s story. He had said he washed his hands in the bathroom sink before calling 911, but DeSanto recalled that first responders told him the sink was dry. “His sink was dry. If he said, you know, he called the police right away, the sink should still be wet,” DeSanto explained, “but it’s very dry in there.”

As O’Donnell looked into Pennig’s background, he learned from Alex’s parents that Alex had struggled in the past with depression and addiction. “I had asked, um, if he had been suicidal in the past, um, and dad said, he had, um, tried, uh, to overdose before,” O’Donnell said. According to Alex’s father, Jim Pennig, a few years earlier, Alex had taken some pills “and told his mother that he was trying to kill himself.” After that, Alex’s parents told the detective that he was sent to rehab, and that he was finally clean. Despite his past struggles, Alex’s parents told O’Donnell that they had just seen him at Thanksgiving. And his mother, Mary Jo Pennig, had just talked to him that afternoon. “He’s doing great,” he said. To him, the idea that his daughter had died by suicide made no sense. “Know your child, it’s not appropriate,” Mary Jo Pennig said.

Since Ecker was the last person to see Alex Pennig alive, the detectives went after him. “He was the only one who could tell us what happened. He was the only one there,” O’Donnell said. They asked Ecker about what happened that night. He said he and Alex Pennig had gone out to some local bars, and when they got back to his place, everything was fine: “We laughed on the way home,” Ecker said. DeSanto asked him if, once he had entered the apartment, he had been fighting. Ecker says they don’t.

DET. ABBY DESANTO: You don’t argue or what?

MATTHEW ECKER: Nope.

DET. ABBY DESANTO: You two, right?

MATTHEW ECKER: Not between us.

For hours, Ecker continued to say that Pennig had locked himself in the bathroom, fired shots and then opened the door to try to help him: “The gun went off behind the closed door … I didn’t shoot him.“

But the detectives were skeptical. Then we got a call from the forensics unit who were still processing the scene. And according to O’Donnell, what he found changed everything. “After Alex was moved, they found a round piece of metal underneath where Alex had been placed,“ she said. “It’s ring-shaped, and about the size of a quarter.” O’Donnell said it was part of the lock of the bathroom door, and the fact that he had found the key in Pennig. “For us, that means the door is open before the shooting.”

Detectives felt the discovery of the metal ring proved that Ecker had lied and had not broken the door open after hearing the shot. Detectives suspected Pennig and Ecker had been arguing and that he had locked the bathroom door to get rid of them. Then Ecker broke open the door, the metal part broke off and fell to the ground, and then he picked up Pennig and he landed on top of it.

Ecker is charged with second-degree murder. In February 2024 he was convicted and later sentenced to 30 years. He appealed his anger.