ST. PAUL — A Minnesota police chief testifying at his officer’s manslaughter trial in the death of a black motorist said Thursday that the shooting might have been justified even if the officer couldn’t see the motorist’s gun.

St. Anthony Police Chief Jon Mangseth was among the first defense witnesses as attorneys for Officer Jeronimo Yanez began presenting their case. Yanez shot 32-year-old Philando Castile five times just seconds after the St. Paul school cafeteria worker informed the 29-year-old officer that he was carrying a handgun.

Castile’s death in the traffic stop last July in a St. Paul suburb drew additional attention because his girlfriend streamed the aftermath on Facebook. A key issue at trial is whether Yanez ever saw Castile’s gun.

Prosecutor Jeff Paulsen asked Mangseth whether his department teaches officers it’s OK for an officer to fire if they can’t see the gun.

“We have to look at the totality of the circumstances,” Mangseth said.

Prosecutors have argued that Yanez’s actions were unreasonable. They have portrayed Castile as being cooperative when he volunteered to Yanez early during the stop, “Sir, I have to tell you I do have a firearm on me.”

Yanez, in squad car video and audio, can be heard in the minutes after Castile’s death saying variously that he didn’t know where the gun was and that he told Castile to take his hand off it. His partner that night testified that Yanez later told him he had seen a gun on Castile, who had a permit for the weapon.

Defense attorney Paul Engh asked Mangseth whether it would be proper for an officer to shoot if a person had his hand on a gun and refused commands.

“It would be very concerning and I would expect action to be taken, given how quickly things can develop,” Mangseth said.

Another St. Anthony officer, Jeremy Sroga, who trains fellow officers in the use of force, testified that a cooperative person can turn into a threat. He also said people who go through training for a carry permit should know to keep their hands on the steering wheel where the officer can see them.

The defense hammered on the theme that Castile made a mistake, calling the firearms instructor where he took a course required for a gun permit. The instructor, James Diehl, testified that students are coached to keep their hands on the steering wheel, then tell an officer they have a permit, then tell the officer they have a gun.

Defense attorneys have argued that Yanez acted reasonably in the presence of a gun and in fear for his life. They have also argued that Castile was stoned at the time of the traffic stop and it influenced his response to the officer.

They called Glenn Hardin, a former supervisor of the state Bureau of Criminal Apprehension’s toxicology lab, to help make the case. Hardin testified he examined autopsy reports to conclude that Castile had smoked marijuana within about two hours of his death. Hardin said his opinion was based on Castile’s blood levels of THC, the high-inducing agent in marijuana.

Prosecutor Jeff Paulsen attacked Hardin’s testimony by citing studies he said concluded there is no reliable way to determine marijuana intoxication from blood samples.