Alex Pareene offers a theory about why the police act as they do:
Having spent many years observing cop behavior, reading news about cops, and occasionally even asking them for help, I have come to a pretty simple but comprehensive answer: They do what is easy, and avoid what is difficult.
Pareene offers several examples later in his newsletter to explain why do police have multiple people arrest someone on a minor misdemeanor while ignoring challenging investigations or not trying to stop a school massacre.