From www.latimes.com: Los Angeles police investigators said Monday they have hit a dead end in their investigation of a mystery motorcycle officer who joined a wild pursuit through the streets and sidewalks of the Westside last week. Senior police commanders spent the last four days poring over personnel and call records, reviewing videos of the pursuit and talking to neighboring police agencies in an attempt to identify the officer, who chased a suspect through Beverly Hills, the Miracle Mile district and Westwood in what officials described as a dangerous duel that put passing motorists and pedestrians at risk. But the detective work so far has left them stumped. The department now plans to bring in a video enhancement expert to break down the images frame by frame, said Assistant Chief George Gascon. The process is similar to that used on videotapes in high-profile incidents, such as last year's police beating of a car-theft suspect in Compton. "It's frustrating," Gascon said. "If it's one of ours, we want to know who it is. If not, there is somebody going through the city and acting as a local law enforcement officer, or worse, impersonating one." Part of the difficulty is that the videos were shot from 1,200 to 1,500 feet above and the motorcycle was going as fast as 70 mph. "It's not like a police car, where there are clear identifying numbers on the top of the vehicle. With our motorcycles, the numbers are much smaller and they are located on the fenders," he said. "All we have at this point is the [TV] video, and we are trying to enhance it." Gascon said he was becoming increasingly doubtful that the pursuer was an on-duty LAPD officer, based on the style of emergency lighting on the motorcycle. But officials in other police agencies denied that one of their officers took part. One theory is that the cyclist was an off-duty or retired officer working on a movie set. Another possibility, Gascon said, is that the pursuer was a private guard who works security for a Hollywood nightclub. "They ride motorcycles that look like a police bike," he said. Investigators believe the pursuer was riding a Harley-Davidson or Kawasaki. LAPD officers primary ride Kawasakis. Security guards for clubs are licensed by the Los Angeles Police Commission and use motorcycles to travel between locations. Gascon said there was a movie shoot in the Hollywood area the night of the pursuit, and that investigators checking if anyone associated with the production might be involved. The chase unfolded on live TV about 10:45 p.m. Thursday. LAPD officers in a police car near Sunset Boulevard and Hudson Avenue started chasing a forgery suspect on a motorcycle. The suspect took off at high speed and drove erratically, leading LAPD commanders, concerned about safety, to end the ground pursuit and leave the chase to a helicopter. At Olympic Boulevard, near Beverly Hills, the unknown officer joined in, tailing the suspect through numerous red lights and weaving through traffic. The unknown officer repeatedly tried to pull ahead of the suspect and cut him off. Those maneuvers forced the suspect to swerve. Twice, the chase went onto sidewalks, which, because of the late hour, were largely empty. Officials said the actions violated numerous department policies and could have endangered lives. Somewhere in Westwood, the unknown officer abandoned the pursuit, leaving the suspect to speed through Santa Monica and then cut back into Palms, Century City and West Los Angeles. The suspect jumped off his bike and ran into an apartment complex in Palms. He remained at large.