Crime Scene Investigation Guide (demonstration in the replay) :

Step #1 - Smash your own face on the countertop
Step #2 - Present a drink to the deceased (as a sign of respect)
Step #3 - Helicopter over to the gun on the floor (which apparently was not the murder weapon)
Step #4 - Check the gun
Step #5 - Realize it is welded to the floor
Step #6 - Have a seizure on the gun (hoping it will un-weld it from the floor)
Step #7 - Realize it is not working and get angry
Step #8 - Kick the door frame multiple times
Step #9 - Smash your own balls on the edge of the countertop

Result of the investigation :

The perpetrator was Martha. She is the only person who had access to the house and a motive for the murder as well.