Thin edge of the wedge
The potential for home invasions exist, even in the statistically peaceful segments of burbs. So if the man of the house hears someone smashing through the front door of his house, his NATURAL instinct is to rush to defend his castle, possibly grabbing a weapon if available.
Thus you have a situation where police SWAT, acting very analogous to home invaders, will burst into a home and be greeted first by a weapon-wielding resident charging towards them. The police, by procedure, do not tase, do not aim to wound. They aim to kill. So when the dust settles and the situation is evaluated, you have a potentially dead head of the household, along with potentially dead other household residents who also acted bravely to defend the castle. There might also be children involved who have now lost their parents.
All of these potentials can be realized by the whim of an informant. Tips from informants can be faulty or malicious, sending SWAT to the wrong home or to the home of someone the information had a quarrel with. The case highlighted in this trailer is one such instance, and represents a microcosm of faulty police diligence followed by ardent deflection of responsibility of authority.