In the surveillance videos of the murders, the killer appears to use a Heckler & Koch USP in 9mm. This type of handgun is also hinted at as the characters call the hand gun am "H&K 9mm".
In the second half on the movie, Terry McCaleb (Clint Eastwood) uses a Remington 870 with synthetic furniture, and extra shotshell holders on the side to shoot at the killer as he flees in the car.
Judging by the foregrip, it looks more like a Mossberg 500 - Swordfish941
Uhhh, no. A Remington 870 can have various pumps, wooden, synthetic, whatever. The ejection port, magazine tube cap, trigger guard, and safety location, and of course various other things show it is without a doubt a Remington 870. - Gunmaster45
At the end of the movie, Detective Ronaldo Arrango (Paul Rodriguez) can be seen with an unknown handgun in his thigh holster (Possibly some kind of Smith & Wesson).
