First, admit that you have a problem. “I’m having a problem finishing this murder mystery story.”
Then, look for a solution.
While looking through past notes for a solution to my reluctance to finishing this short, easy murder mystery story, I found the following website:
How to Write a Book Now
In it, there were seven specific things to consider for the plot.

    Story Goal: what your protagonist wants to achieve

Well – Sam wants to catch the murderer because that is her job and it’s a good thing to do. This story doesn’t have a subplot of why the detective does what she does – mainly for brevity – so there is no reason to ask Why she wants to catch the murderer. Let’s just say she needs to do her job, what motivates her is her job and probably something more personal but we’re not getting into that.

    Consequence: what would happen if the goal is not achieved?

The killer would go on to kill more people. Sam might not do so hot on her next review.

    Requirements: what must be accomplished in order to reach the goal?

Sam needs to find out about the victim, find suspects, determine who the most likely person to be the killer is, and arrest that person.

    Forewarnings: events that signal that the consequence is getting closer

Suspects don’t pan out. More information is needed. A crucial clue is missing or misunderstood.

    Costs: what sacrifices will the protagonist make in order to achieve the goal?

Sam will put herself in danger (which comes in three types – life threatening, job threatening, and sanity threatening).

    Dividends: little gifts that the protagonist earns (related or unrelated) on the path to her goal

Sam is introduced to the shadowy world of the occult (?) which broadens her horizons and makes her a better (?) person.

    Preconditions: little impediments or stipulations that hinder the path to the goal

Sam cannot kill the murderer because she is bound by law to search for justice not revenge.

Something to think about