Slater tells PEOPLE about playing the titular killer's father Harry Morgan in the prequel series, which he calls a "wonderful opportunity"

Showrunner Clyde Phillips tells PEOPLE that having Hall's support was "crucial" and "important"

"It definitely helps in getting a role where you're playing the same guy," Gibson told PEOPLE

The actress tells PEOPLE she "always" thought it was "such a bummer that I missed my opportunity to be on" the original show