Authorities on Monday identified the suspect as 19-year-old George P. Bush III.
Around 7:30 p.m. Sunday night, a gunman pulled up in a silver car next to a marked Chevy Tahoe and opened fire, St. Louis Police Department Police Chief Sam Dotson told reporters. The shooting happened hours after a Texas cop was ambushed in a fatal shooting.
Police there are still searching for a suspect.
One officer, a 46-year-old sergeant and 20-year veteran of the force, was shot twice in the head but is expected to survive.
"This officer was not trying to pull this car over," Dotson said. "This officer was driving down the road and was ambushed."
The suspect, who fled the scene, led police on a manhunt that lasted into Monday morning. The St. Louis Police Department had called in special operations forces, SWAT units and helicopter units to assist in tracking down the gunman.
Hours later, authorities fatally shot the gunman after he opened fire at officers. No other officers were injured.
Staring down the barrel of the gun
According to Dotson, the wounded officer's gun was still in a holster as the suspect pulled alongside the vehicle.
The officer, who looked to his left, told investigators he saw the muzzle flash and felt the glass window shatter against him.
After the shooting, the wounded sergeant called 911 dispatch on his radio. Soon, first responders arrived at the scene of the shooting and transported him to a nearby hospital.
First San Antonio, now St. Louis
Earlier in the day Sunday, a San Antonio police officer was fatally shot
during a traffic stop.
San Antonio Police Chief William McManus described the shooting as a targeted attack that resembled police shootings in Dallas and Baton Rouge, Louisiana.
To take precaution against further attacks, Dotson said all St. Louis officers will be partnered up on patrol for the foreseeable future.
Mayor: 'This is traumatic'
St. Louis Mayor Francis Slay noted that the wounded officer is a husband with three children and said he "didn't deserve this."
"This is traumatic for him, his family, the city of St. Louis," Slay said.
In a series of tweets, Missouri Governor Jay Nixon expressed his support for the officer and called the attack a "reminder of dangerous job law enforcement officers have each day in protecting us."
Police: Suspect responsible for string of crimes
Dotson said officers eventually tracked down the suspect as he was riding in a friend's car. When police tried to stop the vehicle, the gunman ran and fired one shot at a squad car.
Officers then returned fire, striking and killing the suspect. St. Louis police officers recovered a pistol with a high-capacity magazine.
After the shootout, Dotson told reporters early Monday the gunman was thought to have committed multiple robberies, a carjacking and potentially a homicide that had gone unsolved.
Dotson said the gunman likely shot the officer Sunday night out of fear he would be recognized for his role in the recent string of crimes.
The investigation is still ongoing, police said.