Retired Harvard professor cited in fatal July accident

Detlev Vagts, 81, of Cambridge was cited following an investigation by Newton police and State Police. Upon receiving the report, Middlesex District Attorney Gerard T. Leone Jr.’s office charged Vagts with allegedly causing the crash that killed Marcia Kearney, said Cara O’Brien, a spokeswoman for the district attorney’s office.

“With any motor vehicle crash that results in a fatality, there has to be probable cause of criminal negligence to charge the defendant with motor vehicle homicide,’’ she said.

Although he said he regrets what happened, Vagts, who was lost while driving his wife to the dentist at the time of the collision, said that Kearney passed in front of him and that there was no way he could have stopped in time.

“I’ve said before, I’m so sorry it happened,’’ Vagts said yesterday. “I think back on it all the time with sorrow.’’

Investigators said Kearney was traveling west on Ward Street in Newton on a 2005 Vespa GT200 motor scooter at about 2 p.m. July 8 when she used her directional signal for a left turn onto Grant Avenue, Leone said. As she was making the turn, she was struck by Vagts’s car, a 2010 Subaru Legacy sedan, Leone said.

Investigators said that Vagts did not keep to the right of the road and that his car was partially in the opposite lane on Ward Street when he hit Kearney from behind.

The impact threw Kearney about 82 feet. Following the impact, Vagts drove an additional 448 feet before returning to the crash site, Leone said.

Kearney’s sister, Melanie K. Morris of Seattle, declined to comment last night.

Vagts will be arraigned at a later date, O’Brien said. Vagts said he believes the citation to be overly harsh and maintains that the crash was an accident.

“It was just an accident, a sad, sad accident,’’ he said.

Globe correspondent Katrina Ballard contributed to this report. Vivian Ho can be reached at vho@globe.com.