The Niskayuna man who was arrested in September 2023 in a nearly three-decade-old Virginia murder investigation has pleaded guilty to first-degree murder.

Stephan Smerk, 52, admitted on Friday to stabbing 37-year-old Robin Lawrence in her home in Springfield, Virginia on Nov. 20, 1994. Lawrence’s 2-year-old daughter was inside at the time.

Smerk first confessed to the killings last year as investigators were closing in on the case.

DNA evidence was collected at the scene at the time, but investigators said in a news conference announcing the arrest that the technology at the time was limited. There were no matches in the federal database.

Fairfax County investigators began working with a DNA company based in Northern Virginia called Parabon NanoLabs, which developed a family profile DNA and helped track down possible suspects.

Detectives questioned Smerk at his home on South Country Club Lane in Niskayuna in September of last year. He happened to be taking the trash out. Detectives spoke with him and left.

Smerk later contacted them and said he wanted to make a confession.

Lawrence’s sister Mary Cowens spoke to NBC4 in Washington after the hearing.

“For many years, we never thought we would know what happened to Robin. And that was probably the hardest part, not knowing and never being able to put it to rest,” she said.

Prosecutors said Smerk described himself to police as a potential serial killer and he would have killed more people if not for his wife and children, NBC4 reported.

Smerk faces 70 years in prison when sentenced in March 2025.