Don't forget the lady earlier whom said he had cuts on his arm, if this lady is telling the truth then he must be involved.
If he had cuts on his arms (and there is no direct evidence of this yet) there could be many reasons and they could have happened in relation to his job as a mechanic.
That makes me wonder though.
If you are attacking 3 people and you hold the knife, how do you get cuts on your own arms?
If one of the people you are attacking also has a knife, then it might happen. But that is a knife fight, with both holding weapons.
I can see how a right-handed attacker might accidentally cut his own left arm in an attack, but not both arms, as that lady claimed.
Unless we suppose that he had the knife, then the knife was wretled away from him and he was cuts, then he won the knife back again. But that sounds very complicated.
Alternate theory - he went to the house and
he was attacked by someone there with a knife. He got the knife away from the person and stabbed them. Then stabbed the other 2 people as they tried to stop him.