What is the opposite of the expression "have nothing to do with"?

Example: A policeman found a pack of cocaine next to me, but I told him that drug had nothing to do with me. What I mean is: I was not connected to the cocaine at all.

On the other hand, my friend Charles (place the opposite expression here).

What expression is the opposite to "have nothing to do with", considering that my friend is connected to the drug somehow?

Edit: since my first example was a misconception from what I was trying to ask, I brought another context. The asnwers given helped me understand another definition, though. Thanks to everyone who pointed out I was wrong and to those who answered before this edit and helped me anyway.

Solution 1:

My friend's sister and I share a great affinity.

• affinity - A natural attraction, liking, or feeling of kinship, a natural compatibility of one thing with another. TFD

affinity may be followed by of, between, or with.

e.g.

The two of us share a great affinity.

I admire the close affinity of/between Rose and Pam.

I have a special affinity with dogs.

EDIT - Inasmuch as the OP has been changed, I feel I have to provide another answer.

"On the other hand, my friend Charles was involved."

Involved - connected by participation or association: e.g. He was involved in a conspiracy.

Solution 2:

Have nothing to do with means not having an interaction with. I think you mean what you said --- you have nothing in common -- i.e, you share no background, interests, or experience. You may share no interests with someone with whom you deal with every day. For this person who is easy to get along with because you share so much, you may say

My friend's sister and I are simpatico.