"Someone contributing nothing to society killed someone who could have contributed a whole lot," says Brittany Zimmermann's friend Katie Hilton

By Chris Harris
August 13, 2020 10:02 AM
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Brittany Zimmerman
Courtesy Zimmermann Family

Growing up in Wisconsin, Brittany Zimmermann decided early on that she wanted to help people. Specifically, Zimmermann — who loved cats and Japanese anime, and was studying immunology and microbiology — aspired to work for the Centers for Disease Control in Hawaii, where she planned to fight diseases that attack the lungs.

"She said she wanted to get into curing different lung diseases," longtime friend, Katie Hilton, tells PEOPLE in this week's issue. "It would have been great to have her knowledge right now."

Adds Brittany's mother, Jean Zimmermann: "I can only imagine how involved with this COVID-19 pandemic she would have been."

In the spring of 2008, before she was able to graduate from the University of Wisconsin-Madison or realize her many goals, Brittany Zimmermann was viciously killed — allegedly by a drifter with a past conviction for sexual assault, who had broken into the apartment she shared with her fiancé, Jordan Gonnering.

For more on the killing of Brittany Zimmermann and her family's search for closure,  subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

For nearly 12 years, police made no arrests in the case. In March, that changed when 54-year-old David Kahl, who has schizophrenia, was charged by authorities with first-degree intentional homicide.

Jean Zimmermann
Craig Schreiner/Wisconsin State Journal

Long a suspect in the murder, Kahl's arrest owed to advances in DNA science that allegedly enabled police to link him to the crime.

"I always think about how many people she did help and how much good she did, with volunteering, and how much positivity she brought to everyone, and how much good she could have done in her life that was taken away," Hilton, a nurse living in Iowa, tells PEOPLE. "She lost her life and I think about all these people she potentially could have saved during a career, and those people who won't have her going forward. Someone contributing nothing to society killed someone who could have contributed a whole lot."

Kahl has yet to enter a plea to the charge against him. His attorney did not respond to PEOPLE's request for comment.

Prison Letter Yields Break in Case

The killing occurred on April 2, 2008. According to police, Jordan returned from class at around 1 p.m. to find the door to their first-floor apartment kicked in and Brittany unresponsive on the floor. An hour earlier, police say, Brittany's killer brutally beat her before stabbing her in the heart.

In four separate interviews, Kahl allegedly told police he panhandled in Brittany's Madison neighborhood, and ran a regular scam for money to buy crack cocaine. He said he'd approach college-age women, asking for $40 to fix a flat tire. Sometimes, he shadowed his marks, following them into their apartments when they didn't lock their doors. However, for years, Kahl claimed innocence, only admitting to being outside Brittany's apartment at the time of the killing — and fleeing when he heard screaming.

Investigators kept a watchful eye on Kahl, hoping DNA testing on samples from Brittany’s fingernails and clothing would yield clues. Ultimately, the findings were inconclusive.

A break in the case finally came in 2019, in the form of an anonymous letter mailed a decade earlier from Fox Lake Correctional Institution — where Kahl had spent much of 2009 after a parole violation. (He had been convicted of second-degree sexual assault in 1993.)

David Kahl

The letter's author identified several inmates who'd been bragging about their involvement in Brittany's killing. The tip was investigated, but the letter and the envelope it arrived in wouldn't undergo DNA analysis until April of 2019.

Then, last summer, the results allegedly revealed that only Kahl — who has been in prison since 2016, serving a six-year prison sentence following his seventh drunk driving conviction — could've licked that envelope. Subsequent testing on DNA evidence lifted from Brittany's clothing also returned a positive match for Kahl this February, firming up the case against him.

Kahl remains in custody, awaiting trial. A start date for those proceedings is being eyed for mid-2021.

On that horrific day Brittany was murdered, Jean Zimmermann says she missed a call from her daughter — one made minutes before authorities allege Kahl forced his way into her apartment.

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"It haunts me to this day," Jean confides. "I probably would've been on the phone with her when David Kahl broke in — there’s no doubt in my mind."

Jean says she has kept Brittany's legacy alive, in part, with an annual scholarship for students graduating from Marshfield High School and raising money in her daughter's name for the Marshfield Area Pet Shelter, which is building a new facility with a Free Roaming Cat Room named in Brittany's memory. "She may be gone but we will never let people forget who she was, and what she meant to us," says Jean.