(CNN) -- A St. Louis, Missouri, police officer was out of surgery Thursday afternoon but in critical condition after he was shot multiple times while on a traffic stop, a police spokeswoman said.
Spokeswoman Erica Van Ross did not name the 26-year-old officer, but said he joined the department in 2008 and had been a U.S. Marine before that. Van Ross said he was hit six to eight times.
The officer had stopped a vehicle with four people inside, Van Ross said. While he was standing on the passenger side of the vehicle, a male backseat passenger opened fire. The officer returned fire, but it wasn't known if he hit the suspect.
The suspect and two other passengers fled the vehicle, but the driver was still on the scene when other officers arrived. The suspect has not been found, but the other two passengers were caught a short time later.
Police also said the officer's in-car camera system captured the entire incident and that investigators have strong leads on the identity of the suspect.
Three people are in custody, but police were still looking for the shooter, she said.
A witness, David Jackson, told CNN affiliate KMOV-TV of St. Louis that he heard up to 20 shots.
CNN's Sara Pratley contributed to this report