The man accused of killing three people and wounding nine others in a shooting rampage last year at a Planned Parenthood clinic in Colorado was declared incompetent to stand trial at a court hearing on his mental state on Wednesday.

The ruling by El Paso County Judge Gilbert Martinez effectively means a suspension in criminal proceedings against the defendant, Robert Lewis Dear, 58, stemming from the first fatal attack on a U.S. abortion provider since 2009.

The bearded, disheveled Dear, visibly angered at the ruling, called the judge "prejudiced" and a "filthy animal" as he was led out of the courtroom at the end of the 30-minute hearing.

Dear, who has proclaimed himself guilty and a "warrior for the babies" in previous courtroom outbursts, will be transported back to a state mental hospital in Pueblo, Colo., for "restorative treatment," and his status will be reviewed again in 90 days, on Aug. 11, the judge ordered.

Martinez cited the findings of two court-appointed state psychologists who evaluated Dear and concluded he was suffering from a psychotic delusional disorder that they said rendered him mentally unfit to stand trial.

The judge said he was convinced that while Dear could comprehend the proceedings from a factual standpoint, his delusions and paranoia left him unable to meaningfully assist in his own defence.

Martinez ordered Dear to undergo a psychiatric evaluation in December after the South Carolina native demanded he be permitted to fire his attorney and represent himself. Dear has insisted he is mentally competent.

A police detective who interviewed Dear after his arrest and testified at a competency hearing last month recounted Dear saying after his arrest that he harboured a belief that he was being followed by federal agents before the shooting.

Separately, defence lawyer Dan King mentioned in court on Tuesday that his client had smeared himself with his own excrement and drank his own urine from a toilet because he believed the jail was poisoning his drinking water.

Dear has been held without bond since surrendering at the end of a bloody five-hour siege on Nov. 27 at the Planned Parenthood centre in Colorado Springs.

A U.S. Army veteran and a mother of two who happened to be in the waiting area were killed, along with a police officer. Dear has not formally entered a plea. Prosecutors have yet to say whether they would seek the death penalty.