By Colin A. Young Globe Correspondent

Erico Lopez and John Fitzgerald are not your typical crimefighting duo. Instead of tights and capes, they wear suits and ties. They have no secret lair, just their office at the Boston Redevelopment Authority in City Hall. None of that, however, stopped them from fighting crime in Downtown Crossing earlier this week.

While on their lunch break Tuesday, the two 30-year-olds sprang into action when they heard a woman yelling that her purse had been stolen.

“We were just heading to lunch, walking down Washington Street, and we heard a lady yell ‘Thief!’” Lopez said. “She yelled it a couple of times and people were yelling, ‘Catch that guy!’ and all of a sudden there was a guy running by us.”

Faster than the proverbial speeding bullet, Lopez and Fitzgerald followed the alleged thief down the steps of the State Orange Line station. At the bottom of the steps, the man threw the woman’s wallet over a railing, hoping to divert them, but the pair soon cornered him, Lopez said. After alerting a T employee, who called police, Lopez and Fitzgerald had to contain the man until backup arrived.

“Thankfully, he was just kind of sitting there and didn’t really put up much of a fight,” Lopez said. “It was a little uncomfortable. At first, the guy kept trying to squirm by us and was saying, ‘I didn’t do anything,’ but after a while he just sat there.”

Lopez said he and Fitzgerald didn’t think much before they began chasing the alleged thief and that they were both compelled by their “city kid instincts.”

Lopez and Fitzgerald, the son of the late State Representative and activist Kevin W. Fitzgerald, go way back. Both grew up in the neighborhoods of Boston and attended Boston Latin School before heading off to different colleges, Lopez said. Both men were part of the Mayor’s Youth Council, and are now co-workers and roommates.