Partners for about a year, they had responded to dozens of shootings together on the city's violence-plagued south side.
However, the scene they would soon encounter was anything but ordinary.
"It was very chaotic," Conneely said.
"When we first arrived, there had to be about a hundred people out on the street, screaming, crying, people yelling," Conneely recently told CNN. "We had a person shot over here, we had a person shot over there, we had another person shot over here."
The officers found five people shot
, all victims of a drive-by shooting. One of them was 11-month-old Princeton Chew. Princeton's pregnant mother and his grandmother were also shot and lay bleeding on the street.
A woman came running up to both officers holding the baby. Modzelewski knew right away the baby had been shot.
"It's an unreal situation. Borderline helplessness," the 11-year Chicago police veteran said. "You're not quite sure what to do. You want to take action, some kind of action simply because it is a child, and that's pretty much what we did."
The officers broke a department policy, opting to rush the baby to the hospital themselves in their squad car instead of waiting for an ambulance.
Conneely, who has been on the force for 17 years, said that with no ambulance in sight and Princeton losing blood quickly, the two had to take matters into their own hands.
"We both kind of looked at each other and said instinctively, 'We gotta go. Let's go.' "
Conneely snatched the car keys from his partner's hands and got behind the wheel.
Modzelewski, who has a son about a year older than Princeton, hopped into the backseat cradling Princeton, applying pressure to his wound for the roughly 9-mile drive to the trauma center.
"The first thing I did when I got in the car was get on the radio to a firehouse that I knew we were going to pass to see if there was an ambulance in quarters, and when the dispatcher got back to me and said there wasn't, that's when we made the decision to keep going," Conneely said.
His next call was to Stroger Hospital.
"I radioed ahead to them to let them know we were coming in 'hot,' so to speak."
Housing one of the largest and most comprehensive trauma centers in the United States, the hospital's location straddles Chicago's near west and south sides, some of the most violent parts of the city.
Stroger treats thousands of trauma victims every year. Conneely said his partner ran into the hospital and handed Princeton off to emergency personnel who were already waiting and ready to go.
Modzelewski now looks back on how he felt after handing the bleeding baby to doctors.
"It's still kind of a feeling of helplessness because you want to ensure a positive outcome. We stuck around to make sure that happened and luckily, it did," he said.
Princeton's mother and grandmother did not survive, but residents in the Back of the Yards neighborhood where the mother and daughter lived, and died, are grateful for the split second decision made by the two officers.
"I wish his mother and grandmother survived but I'm grateful for what they did for that baby," said Terrell Jackson, who was shot three times in the leg that evening.
The officers' supervisors agreed, deciding not to punish them for violating a department policy.
"They made a decision, and honestly it goes against protocol to remove a victim from a scene unless it's a dire circumstance," a supervisor said. "As it turns out it probably saved a life."
Princeton is now being cared for by family. No arrests have been made in connection with the shooting.
"It's tragic," Jackson said. "When you get older, this is one of those things you'll sadly tell your own kids about."
At a time when high-profile cases of abuse involving police often grab headlines, both the officers are grateful for the chance to keep one young life from being taken by the street, but they quickly downplay any talk of heroism.
"I don't think it's different from what many other men and women in law enforcement do, making a sacrifice. They're on the street in the event a situation like this occurs," Conneely said.
Still, he said "for us to be recognized, we're both grateful. I had a guy, a complete stranger come up to me and say, 'You're the guy with the baby?' I said yeah, and he shook my hand and said, 'Thank you. Thank you for what you did.' "