A riot helmet may have saved the life of a Missouri state trooper after a bullet lodged in his headgear’s face shield during unrest in St. Louis, authorities said.

The Missouri State Highway Patrol (MSHP) shared images of a bullet hole in the shield Tuesday, saying the trooper “narrowly averted serious injury.”

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The trooper was responding to riots that broke out in the city Monday night when a bullet was fired into his moving car, penetrating the face shield of the riot helmet he was wearing, according to the patrol.

A bullet penetrated the helmet of a state trooper responding in his vehicle to Monday night's riots in St. Louis.

A bullet penetrated the helmet of a state trooper responding in his vehicle to Monday night's riots in St. Louis. (Missouri State Highway Patrol)

No further details on the incident were given.

“The Patrol continues to protect Missourians tonight & every night no matter the risks,” MSHP wrote on Twitter.

Following the violence on Monday night, St. Louis imposed a 9 p.m. curfew for Tuesday.

The streets had a larger police presence and there were no large protests after the curfew, the St. Louis Post-Dispatch reported. There were sporadic reports of people disobeying curfew and of a gunshot during a scuffle among a crowd just before midnight.

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Protests during the day in the city remained peaceful, according to the paper.

On Monday night, four police officers were shot during protests in the city’s downtown area, two in the leg, one in the foot and one in the arm.

A retired St. Louis police captain, 77-year-old David Dorn, was also shot and killed by looters while protecting his friend’s pawn shop during the rioting. His body was found on the sidewalk at about 2:30 a.m. No arrests have been made.

David Dorn, a retired St. Louis police captain, was protecting a friend's pawn shop Monday night when he was shot and killed by looters.

David Dorn, a retired St. Louis police captain, was protecting a friend's pawn shop Monday night when he was shot and killed by looters. (Missouri Department of Public Safety)

“David Dorn devoted his career to serving his community as a @SLMPD captain and as @MolineAcres police chief,” the Missouri Department of Public Safety tweeted. “He treated everyone with respect and dignity. His murder is another painful example of the terrible cost crime has on the good people of all our communities.”

Other officers were pelted with rocks and fireworks, and 55 businesses were burglarized or damaged, including a convenience store that burned. Police also shot and gravely injured a burglary suspect who they said shot at officers.

The violence Monday night was sparked by anger over the May 25 death of George Floyd in Minneapolis, which was captured on cellphone video. A white police officer had used his knee to pin down Floyd, an unarmed black man, as he pleaded for air.

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Four police officers were arresting Floyd on suspicion of passing a counterfeit bill. The officers were all fired the following day. The officer who used his knee on Floyd was charged with third-degree murder and second-degree manslaughter on Friday.

The Associated Press contributed to this report.