The day, dubbed "Millions for Mumia" by its organisers, was the latest show of force by a still-spreading campaign set on winning a new trial for Jamal. A former journalist and a leader of the Black Panthers, he was sentenced to death for murdering policeman Daniel Faulkner, 25, during a bloody melee in the city's red-light district.
As police helicopters clattered overhead, demonstrators converged from two directions on City Hall. Chanting "Free Mumia" and "Justice for Jamal", they then marched five blocks south to the corner of Locust and 13th Street where, on the night of 9 December 1981, Jamal, then a taxi driver, intervened in an argument between his younger brother and the policeman.
Jamal - formerly Wesley Cook - has never given his own version of events that night, not even at his trial, which ended when the jury of 10 whites and two blacks found him guilty of killing the officer with two gunshots, one in the back. The deliberations of the jury, drawn from a city whose population is one-third black, took just four hours. His defenders, however, claim that Jamal was not the man who shot Faulkner. Moreover, they contend, witnesses who testified to seeing Jamal firing the shots gave their statements after police coercion.
As the Pennsylvania Supreme Court twice upheld Jamal's conviction - most recently last October - his legend has grown. To the dismay of the city police, the state judiciary, and, above all, Faulkner's widow, who attended an 800-guest dinner in her dead husband's memory on Friday, Jamal has attained the status of a martyr and hero, a symbol of opposition to the death penalty and to a justice system seen as skewed by racial bias.
Adding to the aura of Jamal, who turned 45 yesterday, is his past association with the radical black-rights group MOVE, which secured its own place in history when its headquarters in a Philadelphia terrace house was firebombed by police in 1985, leaving 11 dead, incinerated in the building, and 62 other homes reduced to rubble.
While leftist activists, mainly from New York, provide the intellectual energy for the Jamal campaign, it has been embraced by a much larger spectrum, including President Chirac of France and members of the Japanese parliament. Jamal has also been championed by many celebrity liberals such as Whoopi Goldberg, Ed Asner, Noam Chomsky, David Mamet and E L Doctorow.
Support is spurred in part by free-Jamal web sites on the internet. Leaflets featuring his dreadlock-framed face proliferated like a virus across the US in the weeks leading to the march. A benefit concert in New Jersey in January included performances by the Beastie Boys and Rage Against the Machine.
Jamal, who was within 10 days of being executed in 1995, has himself contributed to his icon status with radio broadcasts from his cell and a book, Live from Death Row, published four years ago. His pronouncements have qualified him as an incarcerated intellectual.
All of which sits badly with many in Philadelphia, for whom Jamal is a reminder of times that were ugly and painful. Even some death-penalty advocates express reticence about a campaign that, they argue, distracts attention from the 3,500 other inmates on the US's death row of whom few have heard.
Amnesty International, while it encouraged people to attend yesterday's events, has not yet taken a position on whether it considers Jamal to have been wrongly convicted.
Emotions were powerful at Friday's tribute dinner to Faulkner. Among the guests was the Philadelphia mayor, Ed Rendell, who shares none of the doubts about Jamal's sentence. "There are hundreds of people on death row in Pennsylvania who have been convicted with less overwhelming evidence than Mumia," he said. "They just don't write poems and Ed Asner doesn't support them."
The deepest frustration is felt by officer Faulkner's widow, Maureen. "So much has been written about the man who took the life of my husband, but lost in those words is Danny," she told the dinner guests. "There are times in my life when I just can't take it any more. I literally get sick over it."
For many in the police, the day cannot come soon enough when the death warrant for Jamal is signed at last. "This individual cold-bloodedly and brutally murdered a Philadelphia police officer," said Rich Costello, president of the Fraternal Order of Police. "He was tried by a jury of his peers and sentence was rendered, and we're expecting that sentence to be carried out".