In 1996, Clark was sentenced to 71/2 to 15 years in prison for a series of armed robberies of women at the Broad Street Line's 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 convicted for driving a stolen car in March 1996 and for robbing three men at gunpoint on South Street in February 1996. He served a 31/2- to 7-year sentence for those crimes concurrent with his sentence for the subway robberies.
In 2009, Clark was charged with trying to break into his wife's apartment and threatening to kill her. The case was dismissed for "lack of prosecution," according to court records. A District Attorney's Office spokeswoman said she believed a witness failed to appear, forcing the dismissal.
On Friday, SEPTA Police Chief Thomas Nestel 3d defended the transit agency's safety record and said Tuesday's attack was "an anomaly."
"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 Avenue and Broad Street to Eighth 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 generally safe, with no incidents reported in December or January, before Tuesday's attack.
Surveillance footage showed a man waiting alone on the northbound platform when a woman walked up and sat on a nearby bench. The woman told police that the man asked to borrow a lighter.
The woman obliged, and the man then grabbed her around the neck and punched her in the face several times. He grabbed her off the bench, dragged her across the platform, and threw her onto the tracks.
The 23-year-old victim was able climb up onto the southbound platform before a train arrived. She suffered bumps and bruises but was not seriously injured.
Authorities said they did not announce the incident immediately to avoid compromising the investigation by describing the suspect's 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 Thursday.
"It was a difficult decision" to keep the attack from the public, but it was the right call, Nestel said Friday.
SEPTA police arrested Clark near 15th Street and JFK Boulevard about 2:30 p.m. Thursday. He was wearing the same jacket, with a distinctive Taj Mahal emblem on the back, and police recovered the victim's cellphone, Nestel said.
Clark was charged with aggravated assault, robbery, theft, simple assault, receiving stolen property and reckless endangerment of another person.
People in Clark's Southwest Philadelphia neighborhood said he was always seen wearing the jacket in the winter.
One neighbor said Friday that Clark appeared angry "most of the time, but I don't think he has any mental issues."
Clark was not seen much on his street but occasionally would walk two little dogs and smoke cigarettes, neighbors said. At his listed address, a woman answered the door and denied knowing Clark, though other people in the neighborhood said Clark lived in the house.
The attack came 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," Nestel said. "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."
See a video of the attack captured by surveillance cameras at www.philly.com/septaplatform
Contact Paul Nussbaum at 215-854-4587 or email@example.com.
Inquirer staff writers Sulaiman Abdur-Rahman and Robert Moran contributed to this article.