Perhaps they bonded over science? Or somebody saved the other one's life?
oh boy oh boy oh boy if Edmund's doing dangerous experiments then total--
waitwaitwait they had to have still been pretty young when they met ANYWAY, though, since Edmund was there during the whole Rosalie thing. I just did maths according the disappearing "shortly after the birth of the couple's first son" so Johnny was about 26 when that happened
and my goodness that's just tragic to think about.
But anyway, by that point they were clearly good enough friends for Edmund to run around risking his life for things that (likely) had nothing to do with him directly, but for Johnny. "Doing his legwork..." Oh, Edmund.
Thus my new theory is they met in a bar. Drunken 21st birthday barfights, unintentional allies, and running from the cops. Shenaningans. Greatness.