Eric Puetz was pedaling home from his bicycle shop in Logan Square on Thursday when he heard a scream and saw some "knucklehead" tussling on the ground with an elderly woman.
That's when the Arlington Heights man sprang into action, riding after the suspect and eventually tackling him.
"Anyone who has a grandma and is put in that situation would react the same," Puetz, 51, said. "It was human instinct."
On Saturday, Chicago police credited Puetz for the arrest of 34-year-old Larry Bostic, who is charged with snatching the 75-year-old victim's purse shortly before 8 p.m. Thursday on the Northwest Side.
By Puetz's account, there was nothing miraculous about what happened. He was riding his bicycle along Pulaski when he heard a woman cry out. Without thinking twice, he said, he darted through traffic and trailed the offender through a maze of alleys. At times, the offender reached into his jacket, repeatedly threatening to pull a gun.
"I was starting to gain confidence because armed robbers don't talk about their advantage over you -- they demonstrate their advantage over you," and no gun was shown, said Puetz, owner of Smart Bike Parts.
Puetz, who had no cellphone with him, tried to keep a safe distance until they reached a parking lot north of Belmont and Karlov avenues with other people nearby.
That's when he yelled for someone to call 911, jumped off his bike, took the suspect to the ground, and held him until police arrived.
"It was an incredible act of courage," Chicago Police News Affairs Officer John Mirabelli said. "We're appreciative; however, we don't encourage people to chase individuals and subdue them. Had it been a case where he did have a gun, the circumstances could have been very tragic."
Mirabelli said Bostic lives a few blocks from where he was arrested. The victim suffered hand injuries but declined medical treatment. Her purse was returned.
For Puetz, who rides his bike 21 miles to and from work each day, there was "much bantering of the 'H' word" (hero) as he spent time with his family Saturday afternoon.
He was having none of it, though.
"All I did is exactly what would be expected from any human being who has common decency," he said. "I'm glad I passed that test. If I failed, I wouldn't want to carry that around."