This is one of BEST way that my students are able to grasp the difference between preterite and imperfect! They LOVE writing police reports!
So, what I do is have a different "crime" or "incident" every day for about 2 weeks. After the incident, students write a police report in the past tense.
I usually have teachers come into class unannounced and unexpected in the middle of class so that the students are surprised and entertained!
This packet includes the police report template, as well as an example police report that I model to the students.