One victim escaped the station and flagged down police, who arrested Andre L. Stovall, 33, after a brief chase.
The girls told police that two men entered the 83rd Street station, 8300 S. Exchange Ave., which is served by the Metra Electric District Line, about 11 p.m. Friday. Both men were armed with knives, police said, and both threatened to kill the girls if they did not hand over their possessions.
Stovall held a 13-year-old against the wall by her neck, according to a police report, while pointing his black-handled knife at a 12-year-old. He said, "Give me your phone and purse, b----, or I will kill you," according to the arrest report.
The girls handed over their phones, but one managed to escape and flag down a passing police car. The sight of the squad car prompted both robbers to flee by jumping off the platform.
Police caught up to Stovall, a college student who lives in the 1100 block of South Springfield Avenue. He faces five counts of armed robbery.
Stovall appeared before Judge Israel Desierto in bond court Sunday, where he was ordered held on $350,000 bail. Stovall, who has another court appearance Friday, will have to post $35,000 to leave jail.