Why is determining the time of death important for criminologists and law enforcement personnel?

Determining the time of death is important in searching for a culprit. They need a time range to find out what suspects were doing around the time of death. This is why often times in crime shows you would hear an interrogator asking "What were you doing at this time on the night of this person’s death?" It is so they can see who had an alibi during the time that the murder happened.