Seriously, put yourself into my situation and be of any use.

[Husar]

You are witness to someone wanting to commit a murder and as Pape said, it's already on the internet. Whether you believe that the police or social workers can talk him out of it is irrelevant, you need to call the police ASAP unless you feel like going to jail for doing nothing. If you notify them and they fail to stop it then it is their fault, if you never say anything it is your fault. And that's both from the law and a moral perspective. How intelligent your friend is is irrelevant, if he has the "better arguments" towards a social worker for why he should murder his father, he will probably still get locked up until he moves away from that idea.

It's nice that you tried to talk him out of it, but now that that has failed, call someone who knows more about this. The police and social workers can also involve psychologists who are about as clever as your friend and have probably dealt with similar situations before, stop pretending that your friend is "too clever for everyone", that's just a dangerous excuse for inaction.

[Beskar]

Contact your local mental health provider or your local police department as soon as possible and say how high the risk is.

Also, your friend has not done anything illegal yet. He has not carried out any plans or made any threats, so having services involved will not affect his standing. But it will help him get the support he needs.