Received email from unknown source containing pornographic images

My friend and I (minors )Received an email from an email id I did not recognise, containing a pornographic picture of a female minor friend, which was edited. I mailed the address back and threatened them that we knew their identity and would report it to authorities if they didn't stop. They mailed back from a different id asking us not to report it and claimed to be closing their account and stopping it. We informed the friend of this later, and she has filed a complaint with Cyber cell. My only concern is that due to being a witness in this case I do not want to be troubled by endless police calls. Victim's parents are aware of the issue. I want her to get justice, but don't want to be caught up in the case. Any advice?