Most murders are not acts of passion or of robbery but incredibly well thought out crimes by well-to-do respectable people who not only kill but frame another and then challenge the investigating detective to prove they did it.
Criminologists are unsure how many serial killers there have been in American history but estimates range from 50 to 300 over the past century with about 10x that in number of victims (cite), but if you watch TV or movies you’ll know that there are many many many moer than that. Miami alone has at least 20 or 30 (though one less with each season finale of Dexter).
Speaking of serial killers, they happen when people have horrible and traumatic incidents in their childhood. That’s about all it takes really.
In some jurisdictions, crime scene investigators and medical examiners are directly involved with the apprehension of at least 99% of all suspects.
In other jurisdictions, they only issue reports from the cages in which they are kept and are occasionally called to testify.
Additionally, the capturing of serial killers is so incredibly time sensitive that despite their relative rarity a private jet is kept on standby at all times to ferry FBI profilers in at a moments notice.
The first suspect to be brought in is never the guilty one.
Service people have incredible photographic memories for stuff that happened weeks ago.
“Yeah, I remember him. He was talking to a blond woman with freckles last Thursday. Then he dropped something down that sewer grate.”
DNA tests take about as long to do as a pharmacist does filling your average prescription.
People are so blase while talking to cops. Usually they don’t even stop doing their chores during it. (folding laundry, stacking boxes, etc) They never say things like, “Holy shit! There was a murder at the end of the block?!! I wait for busses there all the time!! When was this??”
An astonishing number of extremely good-looking women choose careers with the police and the district attorney’s office.
If the police know you committed a crime but can’t prove it, they will devote hundreds of man-hours to harassing you, in the hopes of shaking you up.
Almost every homicide detective has shot at least one assailant, often several. Nearly as many have been shot, stabbed or knocked out at least once themselves. Female detectives have about a 2/3 to 3/4 chance of being abducted and/or nearly raped in the course of their careers.
Every police officer or detective will at some point work on a case that they are personally involved in.
If a witness is in enough danger that they need to be in protective custody, there WILL be an attempt on them: the protective measures will never be purely precautionary.
Any officer who isn’t simply going through the motions until retirement will be suspended at least once in the course of their career.
All cases will be solved someday; if not soon then eventually a clue will turn up and they’ll be pulled from the cold case file and solved.
If the serial killer tends to abduct and torture their victims for a while before killing them, the last one the go after will be smarter than the rest. She will flatter and manipulate the killer, then somehow escape (though none of the others ever even tried). She will get recaptured seconds before the investigators who’ve finally solved the case show up (and are forced to kill him).
All defense attorneys are either a) staunch defenders of the principles of civil liberties and an individual’s right to a fair trial or b) craven publicity whores less interested in defending their clients than turning the entire proceedings into a media circus.
All trials for anything more serious than jaywalking end with an impromptu news conference on the courthouse steps.
Every time a new piece of evidence is uncovered you hear a mysterious “bong bong.”