SEATTLE -- Few clues have emerged in the investigation into the shooting that left a nine-year veteran Seattle police officer killed and a trainee injured on Halloween night, police said.

Investigators on Sunday fielded tips, interviewed potential witnesses and scoured through video tapes for evidence that would lead them to the assailant or assailants. They have not yet identified a suspect or the suspect's vehicle, nor have they determined what kind of weapon was used.

A man described as a person of interest in the killing was ordered held on $30,000 bail -- far less than the $150,000 city prosecutors requested. He pleaded not guilty Monday to a charge of obstruction. More details

Killed in the Saturday night shooting was field training officer Timothy Brenton, 39. Rookie officer Britt Sweeney, 33, suffered a minor injury.

The two were discussing a routine traffic stop while parked in downtown Seattle shortly after 10 p.m.

In a Seattle City news conference Monday, Interim Seattle Police Chief John Diaz said the assailant waited until the traffic stop was completed and then pulled up to the driver's side of the police cruiser so closely that Sweeney was unable to open the door.

Diaz said Sweeney sensed movement and ducked as the shooter opened fire. Brenton died instantly and Sweeney was grazed by a bullet in several places, Diaz said.

The shooter then backed away from the police car and fled, Diaz said.

Sweeney then called for help and returned fire, Assistant Police Chief Jim Pugel said. Diaz said Sweeney may have hit the shooter's car with a gunshot.

Diaz called the shooting a "brutal assassination, a setup," though he said the shooting was believed to be a random act. Pugel said there had been no threats against Brenton and no indication the assailants were looking for him.

Diaz said every camera in the area, including businesses' surveillance cameras, red light cameras and police car video from units in the area is being scoured going back several hours before the shooting, a task that will take hours of manpower.

Four billboards have been donated by Clear Channel that will list tip lines and information about the shooting.

Diaz said every state agency is assisting in finding the officer's killer.

Sweeney was taken to the hospital but was later released and is at home. She joined the force about six months ago, and had graduated from the academy just weeks ago.

Brenton is survived by his wife and two children, ages 11 and 8, officials said. His father and uncle are retired Seattle police officers.

Seattle Mayor Greg Nickels described the shooting as "cold-blooded."

"Our community is in shock at this brutal and senseless crime," Nickels said. "The killing of someone who protects our public safety is universally condemned, and our city is united in rejecting this violence and supporting the men and women in uniform."

Anyone with information can call the Seattle Police Department Tip Line at 206-233-5000, the Seattle Police Homicide Unit at 206-684-5550 or 911. Those who wish to remain anonymous can call Crimestoppers at 206-343-2020 or send a text message to Crimestoppers by texting tip486, then send to 274637. Calls are taken 24 hours a day.

The Seattle Police Officers Guild, along with contributions from citizens and Crimestoppers are offering a total reward of up to $40,000 for information which leads to the arrest and prosecution of those responsible.

In August 2006, rookie officer Joselito Barber was killed when a woman drove her sport utility vehicle through a red light and broadsided his patrol car.

In 1994, officer Antonio Terry was shot and killed after stopping behind a disabled vehicle, according to the Seattle Police Officers' Guild.

On Monday night at 7:30 p.m, St. James Cathedral will celebrate its annual All Souls Day Mass to pray for deceased parishioners and friends and will include special prayers for slain police officer Timothy Brenton, his family and members of the Seattle Police Department.

St. James Cathedral is located at 9th Avenue and Marion Streets in downtown Seattle.

For more information, please contact Corinna Laughlin at 206 622-3559, x3996.

Diaz said Brenton's funeral service will be held late this week or early next week.