But Tom was a lawyer. He even threatens McCluskey that he would have to show cause in a court of law. no one except Michael thought that they could kill a policeman. So whatever Vito's private justice system was, he or his men weren't ready to handle McCluskey outside the court. It was unprecedented, until Michael comes up with his bold plan.
A quick, necessary tactical move by Tom. He needed to make sure that Vito was guarded by trusted men.
I doubt that using the court system was ever in the Corleone's plans to deal with McCluskey in the long run. Tom MAY have been thinking along those lines but as Turnbull pointed out, there was a much more immediate concern for Vito's safety. Once that was assured dealing with McCluskey could be dealt with later.
