Todd, Charles. Inspector Ian Rutledge novels.

"A man is murdered at a society wedding held at Ely Cathedral, and the local police are mystified. In the end, they send for Scotland Yard, but not before another man is killed. This time, there's a witness, but her description of the killer is so strange that no one believes her. So it's Scotland Yard Inspector Ian Rutledge's task to find out who the murderer is and why he has set out on this killing spree, because there is another death, and the three victims are so different that there is no rhyme or reason to their deaths. Nothing logically can connect them. Even as Rutledge begins to close in on the perpetrator, he finds himself doubting his own judgment because the facts are contradictory. It isn't until the fourth murder that something Rutledge witnessed in the war gives him the key and brings back an episode he has tried to forget. But that leaves him with a moral dilemma with only one solution. Will he follow the letter - or the spirit - of the law?"--