In 1996, Clark was sentenced to 7 1/2-to-15 years in Graterford Prison for a series of armed robberies of women in Broad Street subway at the Lombard-South station in March and February of that year.
In each case, he accosted a woman, showed a gun and stole money and jewelry, according to court records.
Clark also was imprisoned for driving a stolen car in March 1996 and for robbing three young men at gunpoint on South Street in February 1996.
He served a 3-1/2-to-7-year sentence for those crimes at the same time as the sentence for the subway robberies.
Clark also was arrested in 2009 for trying to break into his wife's apartment and threatening to kill her. That case was dismissed for "lack of prosecution," according to court records.
On Friday, SEPTA police Chief Thomas Nestel 3d defended the safety record of the transit agency and said Tuesday's attack was "an anomaly."
"We carry up to a million people a day on the SEPTA system, and we rarely have a violent incident," Nestel said Friday. He said the widespread use of surveillance cameras has made it easier for SEPTA police to identify and arrest criminals.
"We're very successful in arresting people," Nestel said. "Hopefully, the bad guys will learn that if you commit a crime on SEPTA, you're going to get caught."
The Broad-Ridge Spur, which runs from Fairmount and Broad to 8th and Market streets, is SEPTA's least-used subway line, with about 8,000 riders a day, and its three stations are often lonely places.
Nestel said the stations on the line are relatively safe, with no incidents reported in December or January before Tuesday's attack.
In Tuesday's attack, surveillance footage showed a man waiting by himself on the northbound platform when a woman walked up and sat on a nearby bench. The woman told police the man asked to borrow a lighter.
The woman obliged and then the man grabbed her around the neck, punched her in the face several times, and violently grabbed her off the bench. He dragged her across the platform and threw her onto the tracks.
The 23-year-old victim was able to get up from the track before a train arrived and walk to the southbound track, where she climbed back onto the platform.
The attacker walked out of the station with the victim's cellphone, police said.
Authorities said they did not announce the incident when it happened because they did not want to compromise the investigation by giving a description of the suspect's distinctive red-and-black jacket.
"It was so distinct that we tried to keep the description of that jacket in law-enforcement circles, because it was our best lead on clearing this," Nestel said during a news conference Thursday. "With our partners in the Philadelphia Police Department, we increased the number of officers out on the platform in our stations, and there were many people looking for this person."
Nestel said Friday "it was a difficult decision" to keep the attack from the public, but he said he thought it was the right call.
SEPTA police arrested the man near 15th Street and JFK Boulevard about 2:30 p.m. Thursday. Nestel said the man was wearing the same jacket, with a distinctive Taj Mahal emblem on the back, and police recovered the victim's cellphone.
Clark was charged with aggravated assault, robbery, theft, simple assault, receiving stolen property and reckless endangerment of another person.
People in Clark's neighborhood in Southwest Philadelphia on Friday said Clark was always seen wearing the distinctive jacket in the cold winter months.
One neighbor said Clark appeared angry "most of the time, but I don't think he has any mental issues."
Clark wasn't seen much on his street but on occasion would walk two little dogs and smoke cigarettes, said people in the neighborhood. Neighbors said he likes dogs.
At his listed address in the 6600 block of Guyer Avenue, near Paschall Playground, a woman answered the door and denied knowing Clark.
But other people in the neighborhood said Clark lives in that house with as many as 15 residents.
In Tuesday's attack, police said they did not have a motive and they said the attacker appeared to be mentally unstable.
The victim suffered bumps and bruises but was not seriously injured.
The attack comes in the wake of two incidents in New York City in which passengers were thrown in front of oncoming trains and fatally struck.
"It is horrifying, and when you see that happen, you think the worst," Nestel said at Thursday's press conference. "We all know there's a tremendous electrical source down there - the third rail. If you touch that third rail, you die.
"Somebody was on her side that day," he added.
Staff writers Sulaiman Abdur-Rahman and Robert Moran contributed to this article.
Contact Paul Nussbaum at 215-854-4587 or firstname.lastname@example.org