How did the first killer of series 2 get into the backseat of a police car without being detected?
THAT is an easy one. It's implied a few times that the killer has his(girlfriend? ex?) help him, so he could have just snuck in quickly when she opened the door to get out, or even have gotten in before any of them entered the car, and the girl just let him hide in the back. It's dark and he was in black clothing.
This may be because I'm an american with no knowledge of the British private school transportation system, but don't they normally discontinue a line of buses before they're sent out to the public?
Couldn't they have used thermal sniping to shoot the killer in the truck in episode 4? They had trained snipers, and they were using amplified microphones to monitor what Luther was saying when he encouraged the killer to put away the dead man switch?
Fridge Horror:At the beginning of season 2, we see Luther playing russian roulette with himself. At first, it just plain out seems that Luther is depressed. But as we go on with the season, we see the full extent of Luther's influence and reputation. His very name killed his wife, drove Ian insane and turned Alice into a weapon. People use Luther to kill and intimidate other people, Luther works outside the law multiple times and people get killed. Even if he's justified, in the end he's achieving some of the same results as the people he's putting away, and he's tired of it. It makes the entire scene with the gasoline in the finale all the more dangerous, and it reveals that the truth is, Luther wasn't just depressed, he was willing to get rid of himself because he saw himself as just as bad.