David Simon: Homicide: A Year on the Killing Streets

The "Homicide Lexicon" and its rules

Throughout the book, Simon frequently refers to a set of 10 informal rules that apply in the majority of homicide cases, as detectives soon learn. They are as follows:

Everyone lies. Murderers lie because they have to; witnesses and other participants lie because they think they have to; everyone else lies for the sheer joy of it, and to uphold a general principle that under no circumstances do you provide accurate information to a cop.
The victim is killed once, but a crime scene can be murdered a thousand times.
The initial 10 or 12 hours after a murder are the most critical to the success of an investigation.
An innocent man left alone in an interrogation room will remain fully awake, rubbing his eyes, staring at the cubicle walls and scratching himself in dark, forbidden places. A guilty man left alone in an interrogation room goes to sleep.
It's good to be good; it's better to be lucky.
When a suspect is immediately identified in an assault case, the victim is sure to live. When no suspect has been identified, the victim will surely die.
First, they're red. Then they're green. Then they're black. (Referring to the color of an open case on the board, the money that must be spent to investigate the case, and the color of the solved murder as it is listed on the board)
In any case where there is no apparent suspect, the crime lab will produce no valuable evidence. In those cases where a suspect has already confessed and been identified by at least two eyewitnesses, the lab will give you print hits, fiber evidence, blood typings and a ballistic match.
To a jury, any doubt is reasonable; the better the case, the worse the jury; a good man is hard to find, but 12 of them, gathered together in one place, is a miracle.
There is too such a thing as a perfect murder. Always has been, and anyone who tries to prove otherwise merely proves himself naive and romantic, a fool who is ignorant of Rules 1 through 9.

- David Simon Homicide: A Year on the Killing Streets