GRAND FORKS (AP) - A man who killed himself and his girlfriend was suffering from mental illness, and he wasn't taking his medications, a pathologist said.

Chad Boeckers, 24, stabbed Tina Torkelson, 26, to death, then stabbed himself to death on Dec. 26, police said. Their bodies were found in the apartment they shared in south Grand Forks.

Dr. Mary Ann Sens, a pathologist at the University of North Dakota and Altru Hospital, performed autopsies on both bodies.

Sens said Boeckers had a history of bipolar disorder and mood swings. He had been admitted to Altru Hospital twice for psychiatric care in late 2006, and was last discharged in October.

Boeckers, originally from the St. Cloud, Minn., area, was 6 feet, 6 inches tall and weighed 280 pounds. Torkelson, who grew up in Park River, was 5 feet, 5 inches tall and 130 pounds, Sens said.

Authorities said he pinned Torkelson to the bedroom floor and stabbed her in the back and through the heart with a 10-inch blade. Then Boeckers lay on the bed and stabbed himself in the chest with the same knife, authorities said.

Torkelson was a nurse and Boeckers was a cardiovascular technician at Altru.

Sens said Boeckers killed himself and Torkelson with knife thrusts directly to the heart.

"I believe he knew what he was doing," she said.

Sens said she could not determine if Torkelson was conscious when Boeckers stabbed her. There were signs of asphyxiation, as if Boeckers was pressing down on Torkelson's upper body or head during the stabbing, she said.

Neither Boeckers nor Torkelson showed signs of alcohol or drugs in their bodies, Sens said.