Revealing mistake: When Frank is on the Jet Ski with the female, chasing after Dimitri, the red strap on its handlebars (with coiled cord) is suddenly attached to Frank's wrist in a close-up, then it's not again. (00:46:20)
Revealing mistake: As Frank is looking at the effects of the virus, a guy jumps him and pulls him through a window. You can tell by the way that they both land that they are jumping onto a covered airbag. (00:51:20)
Revealing mistake: When Frank is pushing Gianni out of the sinking plane at the end of the movie, the surface of the water can be seen, along with the reflection of Gianni's head on it. Since they are supposed to be pretty deep, this can only mean they're in a water tank. (01:18:00)
Revealing mistake: During the garage fight scene towards the end, we see that the steel pole that Frank uses to beat up the bad guys bends while he uses it.
Revealing mistake: Near the end of the movie, the car is driving up to the business aircraft as it is taking off. In one of the flashes of the aircraft, the engine reverse thrusters are engaged. This only occurs on landing. They must have filmed the scene in both takeoff and landing phases of flight, only intending it to look like the plane was taking off.
Revealing mistake: When Lola shoots the police helicopter, it is a noticeably poor visual effects job: the flames appear to merely be superimposed onto the helicopter, and it doesn't look as if the helicopter actually exploded.
Answer: The police will just get in the way and slow things down too much. Frank can operate outside of the law and get more done and get it done quicker. Plus, they can't just take Audrey's word for it.
TedStixon