SAN DIEGO -- A mental competency trial began Monday for a homeless, illiterate ex-con accused of using a stolen flatbed truck to run down and kill a pursuing San Diego police motorcycle officer.

Kevin Williams, 39, could face the death penalty if convicted of murder and special circumstances in the death of Officer Terry Bennett on June 26, 2003.

Last October, Williams was found to be incompetent to stand trial and sent to Patton State Hospital. Doctors there recently determined that Williams' condition had improved and he was returned to San Diego.

Superior Court Judge William Mudd will decide whether Williams is competent to understand the charges against him and assist his attorneys in his defense.

According to court records, Williams was diagnosed with schizophrenia at age 13. Defense attorney Richard Gates said last year that Williams remembers the crash that killed the officer, but his thoughts are scattered and disorganized.

Gates said the homeless man often rambles incoherently and is fixated on religious delusions.

Williams should have been in a locked psychiatric facility and not allowed out in public, Gates said.

But Deputy District Attorney David Hendren said Williams had a long criminal history and twice before had led officers on chases.

Hendren said Bennett started chasing Williams in Encanto. The fleeing GMC flatbed truck contained tools and a generator allegedly stolen by the defendant, the prosecutor said.

Williams made a hard U-turn about 12:30 p.m. and used the truck as a battering ram to ram the officer into a fence, Hendren said.

The competency trial is expected to last four days.