HARRISBURG, Pa. -- A Pennsylvania police officer was charged Tuesday with criminal homicide after investigators concluded she shot an unarmed motorist in the back as he lay facedown after a traffic stop over an expired inspection sticker.

Authorities accused Hummelstown police Officer Lisa J. Mearkle of shooting 59-year-old David Kassick twice on Feb. 2 without legal justification. She was released on $250,000 bail.

Her attorney, Brian Perry, said Mearkle acted in self-defense, and he warned the case could cause police officers to hesitate in high-pressure situations.

"She felt like she had to do what she did," Perry said. "This person was being commanded, begged, 'show me your hands,' and he kept going to his waist."

Authorities said Mearkle had attempted to pull over Kassick for expired inspection and emissions stickers before he sped away. She caught up to Kassick near his sister's home where he had been living for a short time.

He got out and ran before Mearkle incapacitated him with a stun gun, held in her left hand. He was on the ground when she shot him twice in the back with the gun in her right hand, police said.

Mearkle, 36, told investigators she fired because he would not show her his hands and she thought he was reaching into his jacket for a gun. Perry said she did not know Kassick before the shooting.

The offense of criminal homicide encompasses a range of charges, from misdemeanor involuntary manslaughter to felony first-degree murder. Prosecutors often narrow the charge later in the process, about the time when defendants are formally arraigned.

The stun gun contained a camera that recorded audio and video from portions of the encounter, and District Attorney Ed Marsico called it the strongest evidence in the case.

He said it appeared Kassick had been trying to remove the stun-gun probe from his back.

"At the time Officer Mearkle fires both rounds from her pistol, the video clearly depicts Kassick lying on the snow covered lawn with his face toward the ground," according to the arrest affidavit. "Furthermore, at the time the rounds are fired nothing can be seen in either of Kassick's hands, nor does he point or direct anything toward Officer Mearkle."

Marsico said Mearkle waited 4 seconds between the first and second shots, and afterward performed CPR. He called the shooting "a tragedy for all involved."

The district attorney said a syringe was found near Kassick's body, and alcohol and unspecified drugs were found in his system.

Lawyers for Kassick's family and estate issued a statement calling the charges "a substantial step toward closure" after what they described as a horrifying tragedy. They said he had worked as a Teamsters union laborer and struggled with addiction.

"Mr. Kassick is now dead as a result of a traffic stop, a routine traffic stop," said one of the family's attorneys, Christopher Slusser. "He should not be dead. He should not have died as a result of that traffic stop. And the manner in which he was shot -- you can infer from that what you will."

Hummelstown Police Chief Charles M. Dowell did not respond to a message seeking comment, but his department issued a news release that said it had cooperated fully, calling the matter "an extremely difficult case for all involved."

"We are servants of justice and must now allow the judicial process to conduct a fair and impartial review of the allegations that have been presented," the news release stated.

Perry said Mearkle has been on the force for 15 years. She is married to a state trooper and has young children at home, he said. She was expected to be under electronic monitoring.

-- The Associated Press