Investigators say a call to New Hampshire police led them to Jill Kloppenburg’s remains and a murder charge against a Tyngsborough man.

LOWELL, Mass. — A Massachusetts man was held without bail after prosecutors said a tip from a friend led police to the body of missing woman Jill Kloppenburg, buried beneath the garage floor of a Tyngsborough home more than a year after she vanished.

What began as a missing-person case is now a homicide prosecution stretching across two states and several agencies. Prosecutors say Shawn Sullivan, 40, told a friend he had shot a woman named Jill and buried her under the garage floor at the Audrey Avenue home where he lived. Investigators followed that lead, used ground-penetrating radar to identify a cut-and-patched section of concrete, and recovered human remains later identified through dental records as Kloppenburg, a Lowell woman last seen Jan. 2, 2025.

The case broke open on March 10, 2026, when Nashua, New Hampshire, police received a call about a possible homicide. According to Middlesex District Attorney Marian Ryan, the caller said a friend, later identified as Sullivan, had confessed to killing a woman named Jill around January 2025 and burying her under the garage floor. Investigators checked missing-person databases and found Jill Kloppenburg had been reported missing on Feb. 26, 2025. The FBI’s ViCAP bulletin had said she was last seen leaving 735 Broadway in Lowell on Jan. 2, 2025. Police then linked Sullivan and Kloppenburg through their prior relationship and evidence that she had been inside his home around the time she disappeared. By March 15, Tyngsborough police, Tewksbury police and Massachusetts State Police had a search warrant for the Audrey Avenue property.

Investigators arriving at the garage saw what prosecutors described as a large patched area in the concrete floor, about 3 feet by 5 feet. Ryan said radar confirmed an anomaly beneath the slab. Officers cut through the garage floor and recovered a wrapped bag containing human remains. At first, authorities charged the case as the murder of a Jane Doe while the Office of the Chief Medical Examiner worked to confirm identity and cause of death. In court the next day, Assistant District Attorney Ceara Mahoney said dental records had identified the victim as Kloppenburg. Mahoney also told the court that a preliminary autopsy found a through-and-through gunshot wound, with an entry wound to the chest and an exit wound to the back. Those details gave the prosecution its first public account of how Kloppenburg died, though a final medical ruling had not yet been laid out in open court.

The courtroom narrative filled in details that had not been disclosed at the initial news conference. Prosecutors said Sullivan told the friend in February 2026 that the shooting had been accidental. Mahoney said Sullivan later told investigators he was in bed with Kloppenburg in February 2025, holding a gun and drifting to sleep, when he twitched and the weapon fired into her chest. Prosecutors said Kloppenburg died soon afterward. They alleged Sullivan then kept her body in his bedroom for a couple of days, moved it to the garage, dug through concrete, buried her under the floor and sealed the opening with concrete and epoxy. Sullivan’s lawyer argued the account described a “tragic accident followed by inexcusable panic,” not murder, and said the case sounded more like involuntary manslaughter. A not-guilty plea was entered on his behalf.

The case also casts a harsh light on the long uncertainty around Kloppenburg’s disappearance. Friends had told local media in 2025 that they became alarmed when she stopped checking in, saying that was unlike her. Her FBI notice described a 47-year-old woman living in temporary housing with roommates when she disappeared. The delay between her last sighting and the arrest underscores how missing-person investigations can depend on fragments of information that do not make sense until much later. Here, prosecutors say, a year-old death remained hidden until someone who heard an alleged confession decided to call police. It is still not clear from the public record why that caller waited until March 2026, whether anyone else knew what Sullivan allegedly said earlier, or what additional forensic evidence beyond the remains, dental records and the excavation site investigators may present later.

For now, the legal track is moving faster than the search ever did. Sullivan is charged with murder, assault and battery with a dangerous weapon causing serious bodily injury, and improper disposal of human remains. He was arraigned in Lowell District Court on March 17 and ordered held without bail. Prosecutors have not publicly described a motive beyond the account Sullivan allegedly gave, and the defense has already signaled it will contest the level of criminal liability. The next scheduled court date is April 17, 2026. Between now and then, the case is likely to turn on the final medical examiner findings, any forensic evidence recovered from the home and garage, and any statements Sullivan is alleged to have made to the friend, detectives or others. Those pieces will shape whether the prosecution continues to frame the death as murder or whether the defense gains traction with its accident argument.

Outside the legal filings, the story remained rooted in the woman at the center of it. Family and friends had spent more than a year wondering why Kloppenburg had disappeared. Her uncle wrote publicly after the remains were found that he had been notified Sunday evening and was struggling with the news. A friend, Ann Matlosz, had told television reporters during the search period that Kloppenburg always checked in, no matter what was happening in her life. That memory took on heavier meaning after prosecutors described the hidden grave beneath an ordinary two-car garage in a residential neighborhood. On the same street where officers brought in radar equipment and excavation tools, the missing-person posters and unanswered calls gave way to a murder case, a defendant in court and a body finally identified.

For now, the case stands at an early but sharper stage: Kloppenburg has been identified, Sullivan remains jailed without bail, and prosecutors are expected back in court April 17 as the medical and forensic record continues to develop.

Author note: Last updated April 8, 2026.