Prosecutors say a friend’s tip led police to a patched garage floor, a bag of human remains and murder charges against a 40-year-old man.
LOWELL, MA — Human remains found beneath the floor of a Tyngsborough garage are believed to be those of Jill Kloppenburg, a 47-year-old woman missing since early 2025, and a man who prosecutors say knew her has been charged with murder.
The discovery ended a search that had stretched more than a year and shifted a missing-person case into a homicide prosecution. Middlesex District Attorney Marian Ryan said investigators traced the case to a March 10 tip made to police in Nashua, New Hampshire, then used a search warrant and ground-penetrating radar to find what appeared to be a burial site under a garage floor on Audrey Avenue. The remains have not been formally identified, and the state medical examiner is still working to determine both identity and cause of death.
Ryan said at a Monday news conference that the investigation began when a caller told Nashua police that his friend, later identified by authorities as Shawn Sullivan, had said he killed a woman named Jill at his home in or around January 2025. According to prosecutors, the caller said Sullivan claimed he shot the woman and buried her beneath the floor of the garage at the Tyngsborough home where he was living. Police checked missing-person records and found that Jill Kloppenburg had been reported missing in February 2025. Investigators later developed information that Sullivan knew Kloppenburg, that she had been inside his home before, and that he had allegedly been with her around the time she disappeared. On March 15, detectives from Tyngsborough police, Tewksbury police and Massachusetts State Police executed a search warrant at the Audrey Avenue property.
Inside the garage, authorities found what Ryan described as a large patched section of concrete. Local reports said the cut-and-repaired area measured about 5 feet by 3 feet. Investigators scanned the floor with ground-penetrating radar, then broke through the concrete and recovered a plastic bag containing human remains, prosecutors said. Ryan said the victim is being charged in court papers as Jane Doe until a positive identification can be made. Sullivan, 40, was charged with murder, assault and battery with a dangerous weapon causing serious bodily injury, and improper disposal of human remains. Prosecutors have said the remains are likely Kloppenburg’s, but they have also stressed that the identification is not yet official. The Office of the Chief Medical Examiner now faces two central questions that were still unanswered Monday: whether the remains are Kloppenburg’s and, if so, exactly how she died.
The case has drawn attention across northern Massachusetts because Kloppenburg’s disappearance had lingered for months with little public movement. The FBI circulated a missing-person notice saying she was last seen Jan. 2, 2025, leaving her residence on Broadway Street in Lowell. The notice said she was reported missing on Feb. 26, 2025. Ryan said friends reported her missing and had not been in contact with her since late 2024. She was 47. Friends who spoke publicly during the search described her as someone who stayed in touch even during difficult periods, making the silence especially troubling. In October, one friend told local television that the lack of contact was out of character and deeply alarming. That long gap between her disappearance and the break in the case became part of the story on Monday, as prosecutors laid out how a single tip from outside Massachusetts appears to have cracked open an investigation that had otherwise produced no public recovery of her body.
Police and prosecutors also used Monday’s announcement to mark out the procedural path ahead. Sullivan was arrested by Tyngsborough police on Sunday and was scheduled to be arraigned Tuesday in Lowell District Court. Because the remains had not yet been formally identified, prosecutors said the murder charge was filed in connection with a Jane Doe. Ryan said investigators are still treating the matter as active, a sign that more witness interviews, forensic testing and document review are likely ahead. The medical examiner’s work will be central to the case, both for positive identification and for any final ruling on cause and manner of death. Court proceedings are expected to focus first on the initial charges and Sullivan’s custody status, while investigators continue building the underlying homicide case. It was not immediately clear from the reports available Monday whether Sullivan had an attorney prepared to speak publicly on his behalf.
The announcement also brought raw reaction from relatives, friends and neighbors who had spent more than a year fearing the worst. Steven Kloppenburg, the missing woman’s uncle, wrote on Facebook that the family had been told investigators were confident the remains were hers even though DNA testing and an autopsy were still needed. Her family, he said, could now turn its attention to justice and healing. Ann Matlosz, a longtime friend who had spoken during the search, had said in earlier interviews that the silence around Kloppenburg’s disappearance was heartbreaking because she always checked in. On Audrey Avenue, neighbors described a long day of police activity, heavy equipment and workers breaking through concrete. Ella White, who lives nearby, said she hoped the discovery would bring peace to the family. Another neighbor, Joseph McRell, said the arrest was unsettling because Sullivan had seemed ordinary to people living around him. By Monday evening, the house on the quiet residential street had become the center of a homicide case that still leaves key questions unresolved.
For now, prosecutors say the remains are likely Jill Kloppenburg’s, Sullivan is charged, and the case is moving from recovery to courtroom review. The next milestone is the Lowell District Court proceeding and the medical examiner’s findings, which are expected to shape what investigators and Kloppenburg’s family learn next.
Author note: Last updated March 17, 2026.