Michael Tate was sane at the time he killed his friend's father, a psychiatrist testified at his murder trial today.

Although Tate had a history of mental illness, he knew the difference between right and wrong – the benchmark for legal sanity in Colorado, said Dr. David Johnson, who evaluated Tate at the state mental hospital in Pueblo.

Tate is on trial in Jefferson County District Court for first-degree murder in the bludgeoning death of Steven Fitzgerald, 41. He claims he is not guilty by reason of insanity.

Tate, then 16, and Fitzgerald's son, Michael, 17, were runaways from social services when they broke into the Fitzgerald family's Westminster home on Nov. 8, 2004. Fitzgerald testified against Tate last week.

"Obviously Michael Tate has a very disturbed history," Johnson said. "The bottom line is that nobody has ever been able to pin down what's wrong with this kid."

Johnson said Tate had been diagnosed as bipolar, schizophrenic and suffering from post-traumatic stress disorder. Dozens of medications had been prescribed since he was five years old, but none helped, Johnson said. He said some episodes of hallucinations may be attributed to him taking drugs.

Three other doctors testified Friday that Tate showed no psychotic behavior when they observed him for his competency evaluation and during his stay at the state hospital.

The doctors said Tate shows signs of conduct disorder, a precursor of anti-social personality disorder. But they said such a disorder does not mean he is insane.

Psychologist Michael Dial said a mental health test he performed on Tate was invalid because Tate exaggerated his answers, resulting in a "fake bad profile."

"You couldn't have looked more pathologically disturbed than Michael did on that profile," he said. "But there was a marked discrepancy between the test results and the way he looked. I thought Michael was very calculating and clever and could manipulate his environment to suit his personal need."

Dial said such faking is not unusual among those charged with crimes.

"Generally speaking, the more trouble they're in, the more likely you are to get a fake bad profile," he said.