By the time the cashier reported it to SEPTA police, the Market-Frankford train had traveled to 30th Street and the wig-wearing trio were nowhere to be found, Maloney said.
At that time of night, Maloney added that there may have been fewer SEPTA police on duty.
As SEPTA riders express fear for their safety, Mayor Nutter said Commissioner Charles Ramsey was working closely with SEPTA to enhance security.
The three attacks appear to be unrelated, police said.
Maloney called the attacks "real aberrations."
"For years we have been dealing with teens and deploy SEPTA police based on the time of school dismissals. They are usually boisterous and loud," he added. "There's bullying, but now, there's more presence of girls in these things," he added.
On Friday night, the three wig-wearers had boarded the train at 13th and Market streets, and immediately demanded money from the victim. One suspect struck the victim in the face and grabbed $20, before the victim got off at 15th and Market, after only one stop, police said.
After the incident, police said, the victim was transported to Hahnemann Hospital, where he was treated and released for a facial wound.
Police described all three suspects as thin, wearing black pants. Two suspects were about 20-25 years old, between 5-foot-5 and 5-foot-8, with one about 150 pounds and the other, about 160 pounds.
The third offender was slightly older, about 25-to-30 years-old, about 6-feet-tall and 175 pounds, police said.
Wednesday night's victim, Taesha Tazwell, 24, reported her attack by a dozen young adults to a SEPTA cashier at 8th and Market streets. Tazwell said she had been walking through the underground mall when a female suspect stopped her, saying "Excuse me."
Then, she was kicked in the back by a male and fell to the ground, which knocked out a tooth. Her belongings were stolen while she was punched and kicked, she said.
The cashier, who was at track level, and Tazwell saw her attackers get on the Broad Street spur, which runs between Fairmount Avenue and 8th and Market streets. The cashier alerted SEPTA police and five of the 12 were arrested at the next stop. Four more were arrested later.
The incident that prompted the outbreak of SEPTA attacks began on March 26, when Sean Patrick Conroy, 36, a Starbucks manager at the Marriott Hotel, was severely beaten by teens who decided on a whim to try and knock him out with one blow.
Conroy, who had been walking to work through the 13th and Market streets concourse, suffered an asthma attack during the beating and died. Nine teens have been arrested in the incident. *