CHICAGO (CBS) — A warning was sent to Chicago Police officers Monday, after shots were fired at two officers while off-duty this weekend.

As CBS 2’s Suzanne Le Mignot reported, the first shooting took place eastbound on the Eisenhower Expressway at Halsted Street. Fortunately, in that incident and the other one just a few hours later, neither officer was struck by gunfire. Both were in their personal cars.

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In the Eisenhower Expressway incident, a bullet hole was left just below the gas tank on the black Range Rover, and a tire was shredded. The Range Rover was hit several times by bullets while the off-duty officer was behind the wheel Saturday morning around 4:30 a.m.

The 29-year-old officer wasn’t hurt. Illinois State Police troopers searched the expressway for shell casings. Police say the shots were fired from an unknown vehicle.

A few hours later, around 7 a.m., a second off-duty Chicago police officer was shot at while driving near 87th and Halsted streets in Auburn Gresham. The suspect was in a light-colored vehicle. The 28-year-old victim wasn’t injured.

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The shooter fled the scene. It’s not known if these two incidents are related.

Following the shootings, an Officer Safety Alert was issued by Chicago Police. In the alert, reviewed by CBS 2, officers are told to “remain vigilant and aware of their surroundings at all times, both on and off-duty.”

“I applaud the Police Department for alerting their officers of the need to be mindful of their vulnerability to violence, even when they’re off duty,” said Dr. Arthur Lurigio, a professor of criminal justice, at Loyola University Chicago. “This is the season for violence. Summer is when we experience the most incidents of shootings and homicides.”

The officer safety alert also says, “any suspicious activity and/or damage to personal property,” whether “at a department facility or an officer’s residence,” should be documented and reported.

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Illinois State Police are asking witnesses to the shooting here on the Eisenhower to call them. Chicago Police told us the safety alert was issued out of an abundance of caution for officers.

Suzanne Le Mignot