03/11/2013 09:40 EDT | Updated 05/11/2013 05:12 EDT

Criminal expert says Kachkar was 'all over the place'

A leading forensic psychiatrist testified Monday that Richard Kachkar was "all over the place" and difficult to diagnose during an assessment interview, several months after the 46-year-old was arrested for the killing of a Toronto police officer.

Kachkar has pleaded not guilty to first-degree murder in the death of Sgt. Ryan Russell.

The defence is trying to convince jurors that Kachkar is not criminally responsible for what happened to Russell.

Dr. John Bradford, one of the country's leading criminal experts who has dealt with high-profile serial killers such as Paul Bernardo and Russell Williams, told a Toronto courtroom Monday that he struggled to come up with a clear diagnosis for Kachkar.

The five-hour interview with Kachkar, which took place several months after his arrest, was "disjointed," he testified.

When Kachkar was asked about Jan. 12, 2011 — the day he stole a snowplow and he drove it erratically through Toronto streets, striking and killing Russell — he rambled on about a time his in-laws came to visit and ate watermelon, Bradford said.

Doctor stopped short of diagnosing schizophrenia

Bradford stopped short of diagnosing Kachkar with schizophrenia, saying "if there was a more definitive family history, I would be more convinced."

The forensic psychiatrist, however, added "it doesn't mean he wasn't psychotic" at the time of the incident.

In the end, Bradford diagnosed Kachkar with an unspecified psychotic disorder, meaning the accused was not in his right mind.

According to Bradford, Kachkar was not criminally responsible.

In addition to Bradford, two other forensic psychiatrists have testified that Kachkar was suffering from an unspecified mental disorder on the day of the incident. All three of these witnesses were called by the defence.

Bradford is the last witness to take the stand for the defence in Kachkar's murder trial.