In years gone by, about 12, by my reckoning, when I was still involved with rifle shooting..... I had the kit, the training ,and the knowledge for just this kinda job. I would have offered my services for free, even considered it a civic duty to help out.
I'm not going to go into details, but at the time, and probably even now, there are many more riflemen outside the police force who are capable of hitting a 'target' at 600+m...... Some even at 1 mile +
While I support the police, I recognise that they may be limited by kit or training.