A Massachusetts cop is on paid leave for striking a witness who began recording at a motorcycle accident scene on Monday.

Video of  Lawrence cop Alberto Inostroza, a 29-year-veteran, shows him becoming increasingly agitated and losing control then striking witness Michael Centeno, who began recording Inostroza .

Centeno’s friend was involved in the accident, but was not seriously injured.

Inostroza became confrontational with other friends of the motorcycle crash victim who asked for an ambulance and expressed concern about the way a paramedic was handling the victim, according to the Eagle Tribune.

That’s when Centeno pulled out his cell phone and started recording.

When Centeno asks for the Inostroza’s badge number, Inostroza strikes Centeno, knocking the phone from his hand and threatening him with arrest.

“He shoved me and my phone hit my face and I had my hands up in the air and in my head I was just thinking ‘I’m going to get hurt,'” Centeno said.

“I was scared. I kept saying, ‘I’m not touching you.'”

Centeno, who has never had any problems with police in the past, said he respects authority, but wishes Inostroza would have been more professional during the incident.

“I was polite even when he struck me. I respect police officers. I respect authority,” he said.

“I just wish officer was more professional about it.  We did give the paramedics and the officer space. I wish he would have handled it different.”

Lt. Michael Mangan placed Inostroza on leave, according to Lawrence police chief James Fitzpatrick, who said Inostroza lost control and displayed conduct “unbecoming of an officer”.

“There were will be possible discipline, depending on the outcome,” he said, indicating an internal affairs investigation will soon be underway.

“The conduct in the video is not in keeping with the standards of the Lawrence Police Department,” he said after viewing the video, which was emailed to him by a superior officer.

Thus far, Centeno has yet to file a complaint against Inostroza.