Funny stupid student joke

A stupid student was suspended from school .His father complained to the school principal. The principal explained that his son is very stupid and should be suspended. The father denied this, so the principal shouted at the boy: tell me who killed Kennedy. The boy cried: not me. I swear that it wasn’t me. The principal turned to the father and said: did you hear what he said? The father replied: my son never lies and I am sure it wasn’t him who killed Kennedy.It must be someone else from his class.