In the early hours of December 16, 2022, St. Paul homicide detectives Abby DeSanto and Jennifer O’Donnell were called to a downtown apartment to investigate what at first looked like a suicide. Inside the bathroom of her apartment, 32-year-old nurse Alexandra Pennig had been found dead with a single gunshot wound to the head.

It was the kind of case that lingers. Even now, both detectives say they’re haunted by what they saw that morning. Did Pennig take her own life, or did someone else pull the trigger?

When police arrived, they found Pennig’s boyfriend, 38-year-old Matthew Ecker, also a nurse. Initially Ecker said that he was grieving his friend taking her life, emphasis on friend. He didn’t say anything about how the two were dating, secretly. That’s because he was a married father of four. Later, he changed his story, saying that he and Pennig had been seeing each other for about four years, and that she was cool with being his gal on the side.

He told first responders the gun was his, and that Pennig had suddenly grabbed it, locked herself in the bathroom, and fired. “I thought everything was fine,” he said. “And then she just grabbed the gun.” Ecker said he broke open the door when he heard the shot, tried to help her, washed his hands, and called 911.

There were details that seemed to support his version of events. Alcohol and multiple prescription bottles, including antidepressants, were found in the apartment. Pennig’s parents later confirmed she had battled depression and addiction in the past, even attempting suicide years earlier with an overdose.

But there were also troubling inconsistencies. DeSanto remembered that Ecker said he washed his hands after trying to save Pennig—yet the bathroom sink was completely dry. If he’d used it moments before calling 911, shouldn’t it have been wet?

For her parents, Jim and Mary Jo Pennig, the suicide explanation didn’t add up either. They had just seen their daughter at Thanksgiving. Mary Jo had spoken with her the night she died. “She was doing well,” she recalled. “Knowing your kid, it didn’t fit.”

The detectives pressed Ecker. Had they been fighting? Did something escalate? Ecker denied it. “We were laughing on the way home,” he told them. For hours, he stuck to his story: Pennig had locked herself in the bathroom and pulled the trigger.

But then came a breakthrough. Forensic investigators found a small, round metal piece underneath Pennig’s body. It was part of the bathroom door lock. To detectives, the discovery was critical. If the lock piece was trapped beneath her, that meant the door had been forced open before she was shot—not after, as Ecker had claimed.

DeSanto and O’Donnell began to see a different sequence of events. They suspected Pennig locked herself inside to get away during an argument. But when Ecker broke in he unknowingly shattered the lock and the piece fell beneath her. Then, they believed, he shot her.

Ecker was charged with second-degree murder. In February 2024, a jury convicted him and sentencing him to 30 years in prison.

For Pennig’s parents, the verdict brought some measure of closure. But for the detectives who first walked into that St. Paul apartment, the memory of Alex’s final moments—and the truth it took months to uncover—still lingers.