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

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

For detectives, what really happened to Pennig haunts them to this day. And that is the question at the center “The Bizarre Shooting of Alex Pennig” reported by 48 Hours contributor Natalie Morales airs Saturday, October 26 at 10/8c on CBS and streams on Paramount+.

When Detectives DeSanto and O’Donnell arrived at the apartment, they learned Pennig was not alone at the time of her death. There was also a man named Matthew Ecker. Ecker and Pennig were nurses and had met two years earlier when they worked at the same clinic. Ecker told emergency responders that the gun belonged to him and that Pennig grabbed it, locked herself in the bathroom and then fired the shot. “I thought everything was fine,” he said. “And then she just grabbed the gun.” Ecker told emergency services that after he heard the shot, he immediately kicked in 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 did it.

Pennig’s apartment contained alcohol and six bottles of prescription medications, including antidepressants, all prescribed to Pennig. Detectives suggested Alex may have been depressed, so they wondered if Ecker’s story about taking her own life was true.

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

When O’Donnell looked into Pennig’s past, she learned from Alex’s parents that Alex had struggled with depression and addiction in the past. “I asked, um, if she had any suicidal thoughts in the past, um, and my dad said that, um, she had tried to overdose before,” O’Donnell said. According to Alex’s father, Jim Pennig, a few years earlier, Alex had taken a handful of pills “and then told her mom she was trying to commit suicide.” Then Alex’s parents told detectives they sent her to rehab, which eventually got her clean. Despite her previous struggles, Alex’s parents told O’Donnell they had just seen her at Thanksgiving. And her mother, Mary Jo Pennig, was just talking to her that evening. “She did well,” she said. To them, the thought that their daughter had died by suicide made no 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. – Only he can tell us what happened. It was just him there,” O’Donnell said. They questioned Ecker about what happened that night. He said he and Alex Pennig went out to a few local bars and when they returned to her place, everything was fine: “We were laughing on the way home,” Ecker said. DeSanto asked him if there was a fight after he entered the apartment. Ecker said no.

DEFINE. ABBY DESANTO: You guys weren’t fighting or anything?

MATHEW ECKER: No.

DEFINE. ABBY DESANTO: There’s no quarrel between you two?

MATTHEW ECKER: Not between us.

For hours, Ecker said Pennig locked herself in the bathroom, fired a shot, and then kicked down the door in an attempt to help her: “That gun went off behind the closed door… I didn’t shoot her.“

However, detectives had doubts. They then received a call from the forensics unit, which was still examining the scene. According to O’Donnell, what they discovered changed everything. “When Alex was moved, it turned out that there was a round metal piece underneath where Alex was lying,“ she said. “It was ring-shaped and about the size of a quarter.” O’Donnell said it was part of the bathroom door lock, and the key was that it was found under Pennig. “For us, that meant the door had been kicked in before she was shot.”

Detectives said the discovery of the metal ring proved that Ecker lied and did not break down the door after hearing the gunshot. Detectives suspected Pennig and Ecker had an argument and she closed the bathroom door to get away from him. Ecker then broke down the door, the metal part broke off and fell to the ground, then he shot Pennig and she landed on top of them.

Ecker was charged with second-degree murder. In February 2024, he was found guilty and sentenced to 30 years in prison. He is appealing against the verdict.