To be fair and correct: It’s a school district police force (at least, those on site initially were from the school district police force) - not the city police force.
Many school districts have their own police - one of their major normal functions, though, is to ‘handle’ issues that come up so the regular police don’t show up and begin investigations that might lead to hard questions being asked of administrators and leadership. Many are, as a result, very much political.
A heavily armed school district police department. The fire power these people had on that day more than equaled a WW2 US infantry company.
The "School Police Force" appears to be the useless Paul Blart Mall Cop variety - utterly useless.