Lets change up the story slightly and add some mostly irrelevant detail changes:
Two brothers beat up a criminal who is in progress of robbing a bank and cite his race as among the reasons to police.
After some writhing in pain, the jury and the Judge will find the two brothers innocent, and although they shouldn't be racist, they provided a great service to others.
The ethics of the situation hinge on the one detail you left out, just how illegal this person was, and what kinds of impediments were facing police officers preventing them from cleaning up this kind of crime.
This is the same thing that happened with the Trayvon Martin shooting. Though it's not the exactly summary of either situation, it's a truth many people have a hard time thinking through: The phenomenon where it's not OK to stop a home invasion, or any kind of crime in progress if the victim is part of a racial minority.
I'm not defending the brothers actions, justice will serve them up the exact penalty, the issue here is Trump's response, which I agree was wrong, he was siding with lynch mobs and although he wasn't referring to his race, his words can be twisted into a pretzel to make it looks like Trump approves of racial minority violence.
What they did was wrong, but if it turns out the guy was an illegal, then they are a little less wrong. As not-wrong as preventing genocide, and citing race as the motivation. It's possible to be a racist and also totally justifiable in the eyes of the law. Things are not so cut and dry when you really examine things. The brothers were wrong for what they did, and trump was wrong for not condemning them outright. If there was indeed a crime in progress then using violence to confront it while citing racism as the motivation is still wrong, but it's a little less wrong.
Nobody in this story is on the side who's right. Not the victim, the brothers, trump nor the onlookers trying to judge who's right or who's wrong. Everyone here is wrong and the optimal way to settle the matter cannot be realized at this point on account of reddit being in feces flinging mode.