Serial killers study other serial killers, it may be a mutual admiration thing. They are also somewhat of celebrities in jail. I recall being told a story by a guard in the Nassau County lock up, Rifkin was having an argument with Colin Ferguson about who killed more, Ferguson's come back was they Rifkin may have killed more, but they were all women.
Back to the celebrity thing, these inmates may be shunned by other inmates but they are immensely popular with the outside world. Especially with women. I saw an article on the BTK killer, he got more mail than anyone else he was locked up with. Serial killers may be misfits on the outside, but they do revel in their fan base.
Rifkin would be the first guy I would talk with on the LISK case. I don't know if Ridgway was approached for his input. Most of these guys are deep down cut out of the same bolt of cloth.