A popular rock band splits up after the death of a member and a hardworking detective searches for the killer.

Right now your logline doesn't have anything unique popping out. Unfortunately it seems fairly common that a band would break up over a death, and that a detective would be hard working. It may be more interesting if there is a twist, like the detective is lazy, or the last person that saw the band member alive was the detective's girlfriend.

I assume the split up is important because it's rather a stampede (just like when you disturb a nest of roaches by lifting a pebble) and the reasons why it occurs are important for the plot, as well as the fact that the detective must look all around the area (and further afield) to find his killer and some potential victims...

Am I right?

Is the split up of the band important to "Who done it" or is just the murder important.

When a popular rock band splits up after the strange death of a member, a sly and insightful detective searches for the killer in the hope of preventing a hecatomb...

Who is the protagonist here? The hardworking detectve? And what are the difficulties?