Do you have the full sentence? His being involved is similar to saying his involvement but there is an emphasis on the fact that he is involved. It is a stronger way of saying his involvement. It is often used in accusatory speeches like, "What with you being involved!" It is just much stronger than, "Since you're involved!" It is like prolonging the expression into "Since there is the matter of you being involved."

Thank you for your answer. It is good to know it.

Yes.But while both are technically correct, "Everything points to his involvement" is more natural than "Everything points to his being involved." In informal English, the above sentences can sound too formal. "Everything indicates/suggests he was involved" might be better in this case.