ST. PAUL, Minn. (AP) —  A toxicology expert says he believes a black motorist who was shot to death during a traffic stop in Minnesota was under the influence of marijuana.

Glenn Hardin, a former supervisor of Minnesota's state toxicology lab, testified Thursday as a witness for Officer Jeronimo Yanez. Yanez is charged with manslaughter in the death of 32-year-old Philando Castile last July in a St. Paul suburb.

Defense attorneys have argued Castile was stoned at the time of the shooting, which happened in the seconds after he informed Yanez that he was carrying a gun. Hardin said he examined autopsy reports showing Castile's blood levels of THC, the substance in marijuana that gives a high.

Prosecutor Jeff Paulsen attacked Hardin's testimony by citing studies he said show there's no way to determine marijuana intoxication from blood samples.

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A Minnesota police chief is testifying in the manslaughter trial of his officer in the shooting death of a black motorist.

Saint Anthony Police Chief Jon Mangseth was one of the first witnesses as the defense began its case at the trial of St. Anthony Police Officer Jeronimo Yanez. Yanez is charged in the death of 32-year-old Philando Castile during a traffic stop last July in a St. Paul suburb.

Yanez shot Castile five times barely a minute after he approached the car and Castile informed the officer that he was carrying a handgun. Key issues are where Castile's gun was and whether Yanez saw it.

Attorney Paul Engh asked the chief whether it would be proper to shoot a person who had his hand on a gun and refused commands.

Mangseth said such a situation would be "very concerning" and said he would expect "action to be taken."