A Ramsey County judge found a 21-year-old man not guilty of murder due to mental illness after he admitted to strangling his mother and setting the duplex where she lived on fire.

Michael Ray Caldwell, of St. Paul, was charged with second-degree murder last September after he confessed to the killing at a hospital after going there for a psychological evaluation the day after his mother was found dead.

Judge George T. Stephenson issued his verdict in court Tuesday morning. He asked Caldwell, who was dressed in plaid, if he was "taking care of business" at the Minnesota Security Hospital at St. Peter where he is currently. Caldwell replied in the affirmative.

"I'm counting on you to do that," Stephenson said.

Caldwell's mother, Lorine Mary Johnson, 49, was found dead in a first-floor bedroom in September 2012 by investigators after neighbors reported a fire at a duplex on the 900 block of Carroll Avenue. Caldwell admitted to police that he argued with his mother about insurance money before he strangled her and started the fire.

Before her death, Johnson and her boyfriend had flown to Kansas City to get Caldwell from a mental institution. Weeks before, Caldwell had left on a bus to go to school in Oklahoma, but he didn't arrive at the school. Caldwell called and told his mother that he had been kicked off the bus and arrested in Kansas City.

Caldwell had been in a mental health facility, but Johnson wanted him home, so she signed him out against a doctor's advice, according to the criminal complaint.

Nicole Norfleet • 612-673-4495

Twitter: @stribnorfleet