(CNN) -- Law enforcement officials in Seattle, Washington, vowed Sunday to catch whoever is responsible for fatally shooting a police officer and injuring a student officer as they sat in a parked patrol car.
Field training officer Timothy Brenton, 39, was reviewing details of a traffic stop with student officer Brit Sweeney when a vehicle rolled up next to the squad car shortly after 10 p.m., authorities said
People inside the vehicle fired several shots into the squad car, killing Brenton and injuring Sweeney, according to police.
A shot grazed Sweeney, tearing through her uniform and protective vest, Police Chief John Diaz said at a news conference Sunday. She fired at the attackers' vehicle, but police didn't know whether any of her bullets struck it, Assistant Chief Jim Pugel said.
Pugel called the attack an "assassination," but said there had not been a threat made against Brenton.
The attackers' car was a white, light blue or silver sub-compact or compact vehicle, Pugel said.
Nickels described the shooting as "cold-blooded."
"We will not rest until the assailant is brought to justice," Nickels said at Sunday's news conference.
coverage aCrime Stoppers has offered an award of up to $20,000 for tips leading to an arrest and conviction in the case, Deputy Chief Nick Metz said.
Metz said he spoke with the family in the wake of Brenton's killing. Brenton was married with two children, 11 and 8, Metz said.
"The family is obviously extremely devastated," Metz said. "The family obviously at the beginning, when he left for work, certainly didn't anticipate that we were going to come knocking on their door."
Brenton served the force for nine years, police said. His father and uncle are retired Seattle police officers, Metz said.