Updated

A homeless heroin addict acknowledged Monday that he killed a friend's girlfriend after she threatened to expose him for stealing $250 from the cash registers of a dollar store and a gas station.

Anthony Michael Minnick, 27, pleaded guilty to first-degree murder and other offenses stemming from the robberies and the fatal shooting of Sonya Smith, 55, at her rural home near Smithsburg, about 75 miles northwest of Baltimore. Minnick faces a possible life sentence. No sentencing date was set.

Washington County Assistant State's Attorney Brendan Flynn said Minnick shot Smith three times in the head with a .22-caliber, semiautomatic rifle, and then stole her cellphone and a large stereo speaker from the home.

Flynn said Smith was alone in the house she shared with Bradley Roberts when Minnick arrived on the night of May 31, after the retail robberies. Flynn said Minnick had visited the home previously.

Minnick told investigators that Smith told him she recognized him as the retail robbery suspect from store surveillance images police had released to news media earlier that day, and that she planned to call police. They argued, and Minnick shot Smith, according to his statement.

Police arrested Minnick for the retail robberies the next day, June 1, after family members identified him as the suspect. On June 2, Smith's sister, unable to reach her by phone, asked police to check on her welfare at the locked house. They found her body, fully clothed, on a bedroom floor, Flynn said.

Minnick's father told investigators his son was homeless and addicted to heroin, according to court records.

Minnick's lawyer, Assistant Public Defender Amy Taylor, declined to comment after the hearing.