ST. PAUL, Minn. (WCCO) – One day after a St. Paul woman died in an apparent house fire, her 20-year-old son faces a second-degree murder charge for allegedly strangling her and setting her on fire with lighter fluid, authorities say.

St. Paul police found 49-year-old Lorine Johnson’s body early Thursday morning after responding to a house fire at her home on 969 Carroll Ave. Neighbors reported the fire after waking up to popping sounds and breaking glass. They told police Johnson lived there with her son, Michael Caldwell.

According to a criminal complaint:

Homicide investigators spoke with Johnson’s boyfriend, who told them: “I knew I shouldn’t have left her alone with him [Caldwell].”

Johnson’s boyfriend told investigators that on Wednesday he and Johnson flew to Kansas City, Mo., to get her son out of a mental institution. Caldwell wound up there after reportedly getting kicked off a bus and arrested. Against doctor’s advice, Johnson signed her son out of the institution, because she wanted him home.

When driving up from Kansas City, Johnson’s boyfriend said Caldwell’s behavior was odd, “as if he were on PCP.” He said Caldwell was asking questions about where he could find guns, because he feared people were after him. Johnson’s boyfriend told investigators Caldwell “had clearly lost his mind,” and that he was aware of two other instances where he had been violent with his mother.

On Friday, St. Paul Police found Caldwell at United Hospital after an emergency room worker called 911, saying a patient had confessed to murdering someone at 969 Carroll Ave. After being arrested, Caldwell admitted to killing his mother. He said they were arguing about insurance. He said he lit her on fire with matches and lighter fluid.

A preliminary autopsy shows that Johnson’s cause of death was probable strangulation, police said.

If convicted, Caldwell faces a maximum sentence of 40 years in prison.