After Jenna is shot, her body lays in the middle of the road. Later in the film, when it returns to the murder scene, enough time has passed for police to have arrived and cordoned off the immediate area, forensics to have set up base and put on forensic suits, yet nobody has covered Jenna's dead body, as it still lies there in full view of the public.
Shortly after the bombs in the bin fail to detonate, Lexi runs into a phone box. You can hear the sound of coin being inserted when she clearly doesn't put anything in. Besides, emergency calls are free from any phone. She also seems to dial 999 before she has fully lifted the handset.
When Sam and Lexi search the terrorist's hideout in the abandoned prison, we can assume by the dilapidated condition it is in, that it has been abandoned for quite some time. Yet all the lights flick on and off repeatedly, meaning the building still has a supply of electric, which would of been shut off.
After the 2 shoppers witness Sam killing someone, he jumps in the vehicle and speeds off. The terrorist calls the mobile phone and says "2 dead, 2 to go!". This makes 4. The whole premise of the film is 6 murders in 6 hours.