Nearly 37 years after her headless body was found in a river in a remote area of central Illinois, an arrest has made in the death of Diane Marie Riordan Small.

The woman’s husband, Thomas Small, was reportedly arrested in connection to the decades-old cold case. Ms. Small’s body was found under the Airtight Bridge in the Embarrass River, about 130 from her home. Her body was missing the head, feet, and hands — which still have not been discovered. It took 12 years before the body was identified.

According to the Journal Gazette & Times Courier, Small, now 70, was taken into custody on Thursday, and formal charges are expected to be filed early this week.

Authorities have not yet revealed what precisely led to the arrest, but sources with knowledge of the case reportedly told the Daily Journal that Small had admitted to killing his wife — though it is not know to whom he made this alleged confession.

But Small came close to making a confession to police some time ago, according to former Coles County Sheriff Darrell Cox.

Cox told the Journal Gazette & Times Courier that Small seemed to admit to the killing during an interview with investigators several years ago, though it is unclear exactly when. While being questioned, Small reportedly said the presumed killing “wasn’t on purpose.” When further pressed, he refused to continue without a lawyer, and the interview was discontinued.

Cox told the newspaper that Small didn’t say enough to charge him for the murder, but it’s unclear why the investigation did not go forward. At the time of Ms. Small’s disappearance, Mr. Small reportedly called the police some time after October 15, 1980, to report that his wife had left home. Former Bradley police chief Steve Coy told the Daily Journal that Small said in his report that it was not unusual for his wife to leave home for days at the time.

Also unknown is why it took 12 years for Ms. Small’s family to file a missing person’s report, which led to the identification of the body. Until 1992, the victim was known as Jane Doe. After her sister filed a formal missing persons report, detectives were able to identify the body through DNA.

Cole County Sheriff’s office Lt. Christina Stephen told the Journal Gazette & Times Courier that the department re-opened the case in 2012.