Extremely badly behaved child

My friends son is a nightmare. He hits his siblings to the point that they bleed, spits and kicks, swears at them and scratches them including his teachers at school. Recently he began pooing on himself and wiping it all over the room which he shares with his brother (bearing in mind he’s 7 years old) he would wee inside the drawer on his clean clothes.

He also walks in on his sisters whilst they’re getting dressed trying to touch them inappropriately, that happens on a daily basis. He’s also walked in on his mum whilst she’s dressing and tried to touch her. He knows he’s not supposed to do those things but he still does it.

What can she do as his behaviour is out of control. To the point where his siblings even the older ones won’t play with him cos they’re scared he’s gonna physically harm them.

***Update: the school had a therapist come in to speak to the child and assess his behaviour. They also had a chance to speak to him and find out what was going on and he said he behaves that way cos he enjoys it and laughed.

They have had tests done on him and have said he’s got behavioural issues but he’s not on the autism spectrum. She’s also very protective of her kids and doesn’t let anyone look after them but herself, she’s had to stop working because of this. The other kids have told her that they’re scared of him and don’t want him in the house. The school have called her this morning and told her not to bring him in as he physically hurt a teacher yesterday and laughed about it, so they’re scared he’s going to harm another child.

She’s spoken to him to find out why he does it and if he’s being abused at school and he said he wouldn’t cos if anyone tried he would punch them. She has a very good relationship with all her kids and they tell her anything and everything.

Their dad passed away due to illness therefore she’s a single parent.