Step 1. The predictable bones
Cold open: a person we have never met before – usually a woman – goes about their daily life. Their daily life, it would seem, is full of expository dialogue that shows us what a good person they are.
Cut to: a friend / relative letting themselves into the person’s house / apartment, calling out for the person and explaining that they missed an appointment or lunch or class. The friend / relative moves from room to room until they alight upon the person’s dead body.
Cold open: a person or some people are doing something in the woods / park. They spot something out of place and go to look at it. There they discover a dead body.
Cut to: opening title sequence
We open on the main characters at the crime scene, having a conversation about the personal life of one of them. They collect forensic evidence and take pictures, and then the next 53 minutes (including adverts) are spent bringing in and accusing the wrong people of murder (“What about the boyfriend?” “He alibied out.”), receiving results of forensic tests unrealistically fast, and uncovering shocking new evidence just before ad breaks. Eventually they will hit a dead end, until a main character says something unrelated to the case that makes them realise who the murderer is.
The killer is arrested and has his dastardly plan explained to him for our benefit. Then there’s a brief wind-down between the main characters about the earlier personal conversation and we’re out.
Step 2. The tedious meat
Okay, that’s your framework sorted – next, you need your main characters. Should they be just plain old police detectives? FBI? SWAT? ATF? NCIS? A special unit?
Or, if you don’t want the yawn of boring old law enforcement, you could choose from peripheral professions, such as forensic anthropologist (Bones), forensic criminologists (CSI, CSI: Miami, CSI: New York, CSI: Antarctica), coroner (Quincy M.E., The Coroner, Rizzoli and Isles, etc), doctor (Diagnosis: Murder), author (Murder She Wrote, Castle), mathematician (Numb3rs), neuro-psychiatrist (Perception), or college professor (Instinct). Or you could just go nuts and have a main character who can talk to the dead (Medium).
(If you do choose a character from a peripheral profession, make sure you invent a way that they can be in the interview room interrogating suspects even though that would never happen.)
And should your main characters be a man? A woman? Two men? Two women? A man and a woman and some ubiquitous sexual tension? Grizzled detective and rookie? Maybe a team. If you’re feeling extra lazy, make sure you include a character with a photographic memory. At the very least you need a tech nerd who can get around tricky plot points with a spot of hacking.
Then there’s personality, such as it is. You could have cops who don’t play by the rules, cops who have a dark past, cops who are the best at what they do (who don’t play by the rules and have a dark past), self-destructive cops (who are the best at what they do etc). Or your cop / special agent / coroner / doctor / mathematician / neuro-psychiatrist could be an alcoholic, or a recovering alcoholic, or a recovering drug addict, or a pill-popping opioid abuser in denial, or divorced with a kid they never see. Naturally, they’ll be paired with someone more strait-laced and by-the-book.
And finally, there’s location. New York, obviously. Even CSI: Miami was set in New York. But the precinct house / headquarters / coroner’s office / lab should be unrealistically glamorous and televisual. Lots of glass, or exposed brick. A warehouse, a high-tech laboratory, a high-tech medical facility etc. Anything but an office.
Step 3. There is no Step 3
That’s it. That’s all there is to it. Slap a title on it (Cop Police, Special Unit Cop Force, Federal State County Local, Brain Investigation Team, Autopsy Squad or somesuch), use a computer to generate some dialogue and you can get six seasons out of it before one of your main cast leaves. It’s that easy.