Assuming the movie takes place in 2009, the seventh generation Honda Accord (introduced in 2003) seen behind Clyde as Clyde watches Nick shaking Darby's hand during the press conference in 1999 would not have existed.
In the recital scenes, it is obvious that the cello shown on screen is not making the music being heard. At the first recital the bowing does not match, and at the second the finger placement is wrong.
Clyde states that Darby will only do five years for third degree murder, he's technically accurate: that is the minimum sentence for a defendant with absolutely no criminal history. However, Darby already has at least one previous felony, as revealed during the phone call to Darby helping him escape. Under Pennsylvania law, a single felony in the defendant's criminal history would raise that to a 7 1/2 year minimum. Assuming that the judge gave them the 7.5 - 15 year minimum, that would only make them eligible for parole after 7.5 years, no guarantee that they'd be released. Additionally, the judge has the authority to exceed those, and is not bound by any plea agreement.
Detective Dunnigan explains to Nick that the armed robot used API rounds (armor piercing incendiary) ammunition and explains they're anti-tank rounds. Despite being a somewhat accurate description, .50 caliber API ammunition would be unable to pierce modern day tank armor.
As Clyde gives Nick and his legal team until 6:00 to release him the camera shows the clock turning to 6:00 for dramatic effect. Then seconds later when nothing has happened yet Sarah's watch is set five minutes fast.
During the scene where Nick Rice is flying in a helicopter to rescue Bill Reynolds the helicopter has a "N94PD" call-sign on the side of it and the pilot calls out on the radio "N94PD" but when the copter lands it has a "N95PD" call-sign on its side.
In the scene at the abandoned factory Clyde and Darby sit in the police car and it have the small version of the lightbar. When driving out on the road the lightbar have been switched to a bigger version.
When Clyde throws the keys to the cop tied up in the trunk of the police car, he closes the trunk, where a license plate saying "MONTREAL" is clearly visible. The movie takes place in Philadelphia. The Montreal skyline is also visible during many shots.
In the death penalty scene it appears to take place at the Philadelphia prison. However, in the state of PA, all executions take place at Rockview. That prison is located in Central PA, approximately 4 hours to the west of Philadelphia.
Clyde says the venom he uses to inject his second victim with, using the trick gun, is Tetrodotoxin. This venom, known as TTX, is indeed found in puffer-fish (among other sea animals) and can paralyze humans while allowing them to remain conscious. However, the effects take from 20 minutes to four hours to appear and normally include severe respiratory paralysis, especially in large doses. Any person having TTX injected "straight into the bloodstream", as Clyde claims, would suffocate to death within minutes. The only way in which he would have possibly kept his victim alive was by using a mechanical respirator.
During a lethal injection scene three plungers are seen being pressed by a machine to inject the drugs, each in under one second. The largest peripheral venous catheters available have a maximum flow of about 350 ml per minute. The displayed amount of liquids could never have been administered in that short time.
The instant the neurotoxin hit Darby's system he would have fallen down due to being paralyzed. He would not have been able to just stand there, motionless, as muscles are still used when standing still. He also would not be shaking while laying on the table, even when Clyde injected the adrenaline.
Darby is said to have served three years at Marion. Marion Penitentiary is a federal prison, which means that the only inmates there are convicted of federal offenses. Third degree murder (of a civilian, at least) is a state-prosecuted crime, so he would never have been sent to Marion.
When Nick and Clyde are in court before the Judge, Nick repeatedly refers to his government as "The State". Pennsylvania is a Commonwealth and is referred to as such when speaking in the third person in court.
Clyde is arraigned in front of the same Court of Common Pleas judge who sentenced Darby. Cylde's initial arraignment and bail hearing would not take place in the Court of Common Pleas. In Pennsylvania, it would actually take place in front of a local District Justice (magistrate), who would then schedule a preliminary hearing to determine if enough evidence existed to hold the case for trial in the Court of Common Pleas. Furthermore, this would all have taken place before he was ever committed to county jail.
The camera in the interrogation room/cage does not have a cable in it. However, the camera could very well be broadcasting a wireless signal, as any loose cable could be cut/unplugged to break the signal, or used as a weapon in the possession of a prisoner.
When you first see Darby on the table about to be tortured, Clyde moves about the end of the table. as he does he brushes up against Darby's foot and you can see the foot and end of the leg wobble revealing that is is made of rubber.
When Darby is running to the cop car, about 20 minutes into the movie, you can see exhaust from the Police Interceptor coming from the tail-pipes, but when he tells the "cop" to start the car, he turns the ignition to start the motor.
The bomb found in City Hall at the end of the movie is based on Napalm (Malaglinite which is not a real explosive compound). This would have little effect on the structure of the building and would have done nothing more than set fire to the building (as you can see from the final scene). This would give time for the Mayor to escape. The SEMTEX found in Clyde's hideout would have produced the desired result of destroying the building and would have made more sense to use.
After the death of Cantrell, the mayor appoints Nick to be district attorney. The district attorney is a elected county official, not a city official. As such, a city official like the mayor has no jurisdiction over that position in any way, and no authority to appoint anybody or make any decisions regarding that office.
When confessing to the murder of Darby, Clyde says one of the tortures was to cut off his toes with tin snips, yet in the video the first act of torture is to cut his leg off with a circular saw. However, this was probably to invalidate the confession Clyde gave and hence allow him to broker a further deal against a later confession.
When they find the bomb in City Hall, Garza says the bomb has a 30 second delay, but this is just a guess. Nick would have no way of knowing that the 30 second delay was true. So when he confronts Clyde back at the prison, doesn't know when the bomb will function after Clyde makes his final phone call. It could have functioned straight away, killing them both.