When Gerard and the other marshals first interview Dr. Nichols, he tells them flat out Kimble is innocent. He would know. He's the one who framed him.
Kimble takes both guns from the train and dumps them in a US Postal Service mailbox. Meaning that the US Federal Government are the only ones legally allowed to open that box and recover those guns; not the Chicago P.D. That ensures there's no way for anyone to tamper with or take those guns.
While the fate of the two Chicago Police Department detectives who initially investigated Helen's murder, Detectives Rosetti and Kelly, is unknown, it stands to reason that once Kimble is proven innocent that their reputations with their peers and the city would be irrevocably damaged due to their completely stubborn, negligent ineptitude in their pursuit of Kimble and indirectly protecting the real killer, Sykes. When you add the fact that Sykes is an ex-cop, it makes it worse because it might seem to the press like the CPD framed Kimble to cover for one of their own. Plus there's the fact that they tried to kill Kimble and the sniper in the helicopter ended up endangering Gerard on the rooftop. One imagines that Rosetti and Kelly may be suspended, if not expelled, from the CPD as a result of their actions.
The lawyers and judge who prosecuted, sentenced and straight up vilified Kimble would also undeniably look bad as a result of the truth coming out, their own reputations tarnished by the revelation that they tried to have an innocent man sentenced to death for a crime he didn't commit.
Who's to say that some of the people involved in arresting and railroading Kimble weren't aware that an ex-cop was the real killer and were interested in protecting one of their own? Maybe Sykes called in a few favors with his old buddies at the department.
Such as his alibis? May be more likely than Nichols bribing a bunch of his colleagues to vouch for Sykes (he'd want to keep the circle of co-conspirators as small as possible). Whoever they were, they will be charged with perjury one way or another.
In real life, a cop who is found to have planted evidence, coerced confessions, or perjured themselves in one case, will immediately see a great many of every other case they've been involved in seek appeal or be overturned based on their involvement, even if their misconduct was limited to just that one case and all the others were done by the book due to their credibility now being in doubt. Some of Rosetti and Kelly's prior convictions would get thrown out — either genuine bad guys going free, or other innocents who had been falsely imprisoned for who knows how long, or both!
