Mathews tells Williams to get him the make of the car battery from the murder victim's car. This information is later used to determine the time of death based upon how long the horn would blow. It would be useless in a murder investigation since even the same make of battery will discharge at different rates depending upon several factors such as age, the charging system of the car, and the draw of the particular horns. This work was pointless at any rate as the coroner would quickly determine the time of death via the temperature of the body.
It is impossible to tell the gender of a person from fingerprints.
A fake siren such as the one stuck on top of the fake police car would not make any noise.
As Dan Matthews and Sgt. Williams are catching up to Harvey Talbot's car Freddy spots the approaching Chevrolet unmarked undercover car. He immediately yells to Nicky and Casey "it's the cops". There would have been no way he could have known at that distance that the approaching car was occupied by cops.
When Dan calls in the APB on Harvey Talbot he gives the dispatcher a complete physical description from Talbot's drivers license including his drivers license number which would have been useless to officers. However he never gives a description of his vehicle which he had just seen.
Mathews wastes time by calling in an APB on the victim that had dropped his wallet. Since only 60 seconds had passed since the car had passed him, he and Williams could have easily overtaken the car, especially since Garvey had told the driver where to turn. Instead of doing this, he and Williams go in another direction.
At the roadblock, Garvey tells Mathews and Williams about the man dropping his wallet. He says it is the car that just passed them as they arrived, but he never described it. Matthews asks him "It's a blue convertible, you say?" and Garvey says "That's right." Garvey never said anything descriptive about the car.
When Williams dials the phone to check on the detour sign, he dials only 5 digits instead of the 7 required.