The discovery beneath a Tyngsborough garage ended a long search and moved a Lowell woman’s disappearance into a murder case.
TYNGSBOROUGH, Mass. — For more than a year, Jill Kloppenburg was a missing woman on flyers and federal bulletins. This week, prosecutors said her remains were found beneath the concrete floor of a garage, and a Tyngsborough man was charged with her killing.
That shift changed the meaning of nearly every known fact in the case. Kloppenburg, 47, had last been seen leaving her Lowell residence on Jan. 2, 2025, and was reported missing on Feb. 26, 2025. Friends said her silence was out of character. The FBI posted a ViCAP alert. Then, on March 10, 2026, a call to police in Nashua, New Hampshire, redirected the investigation. Prosecutors say the caller reported that Shawn Sullivan had admitted killing a woman named Jill and burying her beneath the garage floor at his Audrey Avenue home.
Before the arrest, the public story was mostly absence. Kloppenburg left 735 Broadway in Lowell and never returned. The federal missing-person notice described her as 5-foot-3 and 120 pounds, with brown hair, blue eyes and identifying tattoos, the kind of details authorities publish when they are still hoping to locate someone alive. Friends told Boston-area television reporters in 2025 that they reached out to police because Kloppenburg always checked in. Her disappearance sat in that painful category of unresolved cases where family and friends are left to read silence, rumors and passing months. By the time police say the new tip arrived this March, the case had already crossed the one-year mark. What had been treated publicly as a missing-person search was, prosecutors now allege, a concealed homicide from the start.
The breakthrough came not from a random search but from an account police say someone chose to share. Middlesex District Attorney Marian Ryan said the Nashua caller told police a friend had confessed that he shot a woman named Jill in or around January 2025 and buried her beneath the garage floor. Investigators checked missing-person records and focused on Kloppenburg. They say Sullivan knew her, had been with her around the time she disappeared and had her inside the Audrey Avenue home. On March 15, detectives from Tyngsborough, Tewksbury and the Massachusetts State Police searched the property. There, Ryan said, they found a visibly patched section of concrete. Ground-penetrating radar showed a buried anomaly beneath that spot. Officers cut into the floor and recovered a wrapped bag containing human remains.
By the time Sullivan appeared in Lowell District Court on March 17, the body recovered from the garage had been identified through dental records as Kloppenburg. Prosecutors used the hearing to describe what they say happened inside the house before the burial. Assistant District Attorney Ceara Mahoney said Sullivan told investigators he was holding a gun while he and Kloppenburg were in bed in February 2025, began drifting to sleep, twitched and fired the weapon into her chest. Mahoney said Sullivan told police Kloppenburg died soon afterward. Prosecutors said he kept her body in his bedroom for a couple of days, then buried it below the garage floor and covered the spot with concrete and epoxy. A preliminary autopsy, Mahoney said, found a through-and-through gunshot wound. Those details transformed the case from a mystery about where Kloppenburg went into an argument over how criminally responsible Sullivan is for her death.
That argument surfaced immediately. A not-guilty plea was entered for Sullivan, and his lawyer described the shooting as a “tragic accident followed by inexcusable panic,” urging the court to view the case as involuntary manslaughter rather than murder. The judge ordered him held without bail. Sullivan also faces charges of assault and battery with a dangerous weapon causing serious bodily injury and improper disposal of human remains. Publicly, though, much remains unsettled. Prosecutors have not outlined a broader motive. They have not explained whether the gun was legally possessed, whether anyone else was in the house at the time, or what physical evidence from the bedroom, garage or firearm testing may be introduced later. The medical examiner’s final findings also remain important as the prosecution and defense frame intent, causation and timing.
What makes the case especially stark is how ordinary settings can hide extraordinary violence. The key location was not a remote field or wooded lot but the garage floor of a home on a residential street. Kloppenburg’s case passed through missing-person databases, local police channels and a federal bulletin before detectives finally cut into concrete at a house where prosecutors say she had once been a guest. The story now sits at the meeting point of two familiar realities in criminal cases: the long, grinding uncertainty for the people left behind, and the sudden acceleration that can come when one witness decides to talk. Family and friends who had spent months hoping for contact instead received confirmation that the search had become a homicide case.
For Kloppenburg’s relatives and friends, the discovery answered the hardest question and opened several more. Her uncle said publicly that police notified him Sunday evening after the remains were found. A friend who had helped sound the alarm during the missing-person phase later spoke in grief and anger after the arrest. Their voices are not legal evidence, but they help explain the human timeline running beneath the court calendar: Jan. 2, 2025, the last sighting; Feb. 26, the missing-person report; March 10, 2026, the tip; March 15, the excavation; March 17, the arraignment. A year of waiting ended not with a reunion, but with an identified grave and a defendant held for trial.
The case is now set to return to court April 17, when prosecutors are expected to continue building the record around Kloppenburg’s death and the burial beneath the garage floor.
Author note: Last updated April 8, 2026.