(CNN) A police officer in Maryland was charged with murder after authorities say he shot an unarmed man seven times while he had him handcuffed inside his police cruiser.

Prince George's County Police Cpl. Michael Owen Jr. is also facing manslaughter and associated weapons charges in the fatal shooting of 43-year-old William Howard Green in Temple Hills, Maryland, police said.

Prince George's County Officer Michael Owen Jr. was arrested Tuesday.

"I'm unable to come to our community this evening and provide you with a reasonable explanation for the events that occurred last night," Prince George's County Police Chief Hank Stawinski told reporters. "I have concluded that what happened last night is a crime."

Monday, Owen and another officer responded to reports of a car slamming into parked vehicles, CNN affiliate WJLA reported , citing a police spokeswoman.

The officers found Green -- the car's driver -- and handcuffed him. They believed he was "under the influence of a substance" and called for "drug recognition expert," police said in a statement.

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