It happened early Friday morning before the area was filled with shoppers.
"We were driving by and heard a loud scream or shriek," said. Chris Frieden.
"I yelled at the guy, and I saw him grab the purse and took off, and I just took off after him," Mike Hochhauser said.
"She was laying on the floor and i stayed there 'til the police arrived," said Angela Deleon.
All three good Samaritans didn't hesitate to help once they realized that a woman had just been attacked.
While Deleon called 911, Hochhauser and Frieden ran after the suspect.
"We continued to chase him, lost his trail when he turned the corner and went down another road near the Hancock Center, and then went into an alley," Hochhauser said. "And at that point we were quiet and waited, and he did come out.
And the chase was on again. The suspect tried to get into a cab and get away, but the two men got the driver's attention and he stayed put, trapped in the cab.
"Chris blocked one side of the door, I got the other, and at that point, that's when the cops came and did their thing," Frieden said.
"As soon as we pulled up, we saw two citizens standing next to a cab yelling the robbery offender's in here," said Chicago police officer Patrick Bryant.
That's when the officers arrested Richard Mendoza.
Mendoza, charged with robbery and battery, was on parole and was wearing an ankle monitoring bracelet at the time.
Police credit the good Samaritans for coming to the woman's aid.
"I would definitely not recommend everybody do that, but if more citizens got involved as they did, there would be a lot less crime in the city," Bryant said.
"If something would happen to me, my mom or my sister, I would want someone else to do the same, try to help out."
Hochhauser said the woman had a black eye and other injuries, but she thanked him for helping her.
Police are urging women to hold their purses close and high on their arms while shopping.