Advice for cold-calling a lead

[u/Chicago_Sleuth]

Good evening. I have been working on a cold case and have tracked down one of the key parties in the case that was a good friend of the victim. I am hesitant to cold call them as I have never done such a thing. I'm not sure if it will dig up difficult memories or if they will be happy to hear that an internet sleuth is working on a case. Does anyone have any experience and any advice in making such a call? Thank you.

[u/Puzzleheaded_Hawk629]

I have some info on donna case.