Same thing at Ruby Ridge. At one point, prior to the siege, a surveillance unit had broken down. Randy Weaver pulled over by the car to ask if the guys needed assistance.
They could easily have made an arrest at that time, and I would be amazed if they didn't have other opportunities to make an arrest in the middle of nowhere.
Instead, they laid a siege, and killed a dog, a teenager, and the mother of an infant (as she was holding the infant).
Edit: The irony of this is that, at least for the last many years, the military makes serious attempts to go after targets when they are not near potential collateral damage. If the military is more cautious about harming innocents than LE are, that's unnerving in itself.