How a small piece of a bathroom door lock helped solve a nurse’s murder

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

For the detectives, what really happened to Pennig is something that still haunts them to this day. And it is the question that is central “The Strange Shooting of Alex Pennig,” reported by “48 Hours” contributor Natalie Morales. The episode is now streaming on Paramount+.

When Detectives DeSanto and O’Donnell arrived at the apartment, they discovered that Pennig had not been alone at the time of her death. A man named Matthew Ecker was there too. Ecker and Pennig were both nurses and had met two years earlier while working at the same clinic. Ecker told first responders that the gun was his and that Pennig had grabbed it, locked himself in the bathroom and then fired the shot. “I thought everything was fine,” he said. “And then she just grabbed the gun.” Ecker told first responders that after hearing the shot, he immediately broke down the bathroom door: “I tried to do what I could. And then I washed my hands… That’s why I have nothing on my hands.” Ecker said he then called 911. But it was too late. He said he didn’t know why Pennig would do this.

Inside Pennig’s apartment were alcohol and six bottles of prescription medications, including antidepressants, all prescribed to Pennig. To the detectives, this suggested that Alex may have been depressed, and they wondered if Ecker’s story that she had committed suicide was true.

But they also noticed something that seemed to contradict Ecker’s story. He had said he washed his hands in the bathroom sink before calling 911, but DeSanto recalled first responders telling her the sink was dry. ‘The sink was dry. If he had said, you know, he would have called the police right away, that sink probably would have still been wet,” DeSanto explained, “but it was very dry in there.”

When O’Donnell looked into Pennig’s background, she learned from Alex’s parents that Alex had struggled with depression and addiction in the past. “I had asked if she had been suicidal in the past, and Dad said, she had tried to overdose before,” O’Donnell said. According to Alex’s father, Jim Pennig, several years earlier, Alex had taken a handful of pills “and then told her mother she was attempting suicide.” Afterwards, Alex’s parents told detectives they sent her to rehab, and she eventually got clean. Despite her past struggles, Alex’s parents told O’Donnell that they had just seen her on Thanksgiving. And her mother, Mary Jo Pennig, had just spoken to her that evening. “She was doing well,” she said. To them, the idea that their daughter had committed suicide did not make sense. “Knowing your child, it didn’t fit,” Mary Jo Pennig said.

Because Ecker was the last person to see Alex Pennig alive, detectives focused on him. ‘He’s the only one who can tell us what happened. He was the only one there,” O’Donnell said. They questioned Ecker about what happened that night. He said he and Alex Pennig went to several local bars, and when they arrived at her home, everything was fine: “We were laughing on the way home,” Ecker said. DeSanto asked him if once they entered the apartment they had gotten into an argument. Ecker said no.

For hours, Ecker continued to say that Pennig had locked herself in the bathroom, fired the shot, and then broke down the door to help her: “That gun went off behind a closed door… I didn’t shoot her.”“

But the detectives had their doubts. Then they received a call from the forensic unit who were still processing the scene. And according to O’Donnell, what they found changed everything. “Once Alex was moved, they found a round metal piece underneath where Alex had been lying,“ she said. It was shaped like a ring and about the size of a quarter. O’Donnell said it was part of the bathroom door lock, and the fact that it was discovered under Pennig was the key. “For us it meant the door was broken down before she was shot.”

Detectives believed that the discovery of the metal ring proved that Ecker had lied and not broken down the door after hearing the shot. Detectives suspected that Pennig and Ecker had had an argument and that she had locked the bathroom door to get away from him. Then Ecker broke open the door, the metal part broke off and fell to the ground, and then he shot Pennig and she landed on top of it.

Ecker was charged with second-degree murder. In February 2024, he was convicted and later sentenced to 30 years. He is appealing against his conviction.

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