Although Harrison, 36, admitted to members of Central Detectives that he had been in the fight, he insisted that he had nothing to do with the shooting, the sources said.
His handlers maintained his innocence during the ensuing media firestorm.
The case eventually stopped generating headlines, and Harrison returned to his lucrative day job as a wide receiver for the Indianapolis Colts.
But over time, the investigation uncovered evidence that seemed to point in Harrison's direction:
* Harrison and Dixon squabbled for two weeks before the shooting after they exchanged words in Playmakers, a bar on 28th Street near Cambridge that Harrison owns.
* Ballistics tests proved shell casings found at the shooting scene had been fired from Harrison's gun, a Belgian-made FN5.7, law-enforcement sources said.
* Detectives found the firearm in Harrison's garage on Thompson Street.
* Witnesses and Dixon separately identified Harrison as the shooter, the sources said.
The lawsuit, filed Sept. 2, is worded in a way that would find Harrison responsible regardless of the outcome of the criminal investigation.
"The defendant intentionally and outrageously shot the plaintiff," reads one portion of the lawsuit, while another section states that Dixon, 32, was shot by someone else who used Harrison's gun.
"Look, it's our position that Marvin Harrison was the shooter," said Robert M. Gamburg, Dixon's attorney.
"But even if you believe the other theory, Marvin's gun was still used in the shooting, so he was negligent for leaving the weapon where someone else could obtain it."
The lawsuit further claims that Dixon, who was wounded in the left hand, suffered "serious and permanent injuries . . . and a severe shock to his nerves and nervous system," according to a copy obtained by the Daily News.
The suit seeks more than $100,000 in damages.
Harrison's attorney, Daniel J. Hart, and his agent, Tom Condon, did not return repeated calls from the Daily News.
Gamburg said it will likely be months before Harrison, Dixon and others involved will be called for depositions.
"It'll be interesting, to say the least," Gamburg added.
"The question is, will his attorney assert [Harrison's] Fifth Amendment privilege against self-incrimination?"
But another wrinkle in the case will arise on Nov. 17, when Dixon is due in court to face charges of making a false report to police.
A few hours after the April 28 shooting, Dixon turned up in Lankenau Hospital, in Wynnewood, where he initially told detectives that he had been wounded while driving in West Philadelphia, sources said.
Dixon later recanted and identified Harrison as the shooter, the sources said.
"It's kind of bizarre," Gamburg said.
"The authorities must know what really happened, because how else could they charge him with lying about where he was and who was involved?"
Assistant D.A. Diviny declined to discuss the investigation into the shooting.
Dixon told investigators that he and Harrison grew up near each other in North Philadelphia, where Harrison eventually made a name for himself as a two-sport standout at Roman Catholic High School, sources said.
He went on to star alongside future Eagles quarterback Donovan McNabb at Syracuse University and then found fortune and fame in the NFL. Harrison signed a $67 million contract extension in 2004, and helped the Colts win the 2007 Super Bowl. *