Guilt over not being able to stop it

[ShatteredWings]

...x

[Oblivion]

Try telling your school counselor or the police.
They don't take this lightly, especially if he has a bruise.

[ShatteredWings]

...x

[Oblivion]

You do have something to go on.
You saw your mom abuse your brother and he has a bruise
Child abuse+Proof=Cops

[Sapphire]

You probably feel guilty because (I'm assuming that he's younger) you are older than him and are generally more responsible. There are things you can do to help him, but in this current situation that you have described very little will occur in terms of consequences.

If you aren't sure who gave him the bruise then I'm not sure if you should say anything this time round. If something happens again and you see him getting injured by your mum then you should go to the police or you know that she injured him. The police don't dismiss things like that, especially if there is an eye-witness.

[ShatteredWings]

...x

[thesphinx]

Ok I think what you should do is go to the police station explain the whole situation and tell them before hand that your mom is going to make excuses.
Then as you are still there (so you get the same people) have them get your mom to come to the station.
You have sufficient proof so they should believe you.

[Sapphire]

Does this happen frequently?

[ShatteredWings]

...x