[header] How to write murder mysteries [title] Read as many murder mysteries as you can as it will expand your knowledge. [step] The more you learn about them, the better. By watching murder mysteries as well as reading them you may gather some ideas about how murders are solved. 
Watching real life cop shows may also help. If you are serious about writing and can get the permission, it may be a good idea to shadow a detective team or at least ask them how murder investigations work.