Aurora police said Saturday an officer who was shot during a traffic stop is expected to survive as the search continued for the person who stole an unattended car and shot the officer.
Another officer returned fire Friday night, but it was not known if the suspect was wounded.
Authorities said the officers did not know that the driver had just stolen the car a few blocks away after the owner had started the car and left it running unattended, the Denver Post reported Saturday.
The wounded officer was taken to University of Colorado Hospital where he was in surgery for several hours.
He was in serious but stable condition and is expected to survive, according to a tweet by Aurora police. The officer's name has not been released.
The vehicle was found abandoned in the middle of the street several blocks away.
"We have no clue where this individual is," police spokesman Frank Fania said Saturday.
So-called "puffer" cars belching exhaust are left by drivers running unattended, usually in cold weather. Leaving a vehicle unattended is illegal. There was no information Saturday on what, if any, charges could be filed against the person who left the vehicle running.
Police warned residents of the neighborhood to stay in their homes and call 911 if they saw anything suspicious.
Denver police and Jefferson County authorities assisted Aurora police. Dozens of officers flooded the area, searching cars and knocking on doors. A helicopter was called and police K-9 units aided in the search.
Fania said police are now going over records of possible suspects.