Rosie Larsen and Growning Pains

So I'm addicted to the AMC show, The Killing. The Killing follows the murder investigation of Rosie Larsen. So I'm watching this one episode and I keep thinking I know one of the actors that is playing the wife of a suspect.

I'm like "where have a seen her before. Then it hits me. That is the girl that played Chrissy Seaver on the T.V. Show, Growing Pains. (Played by Ashley Johnson)

Chrissy was the youngest of the Seaver clan. Just like all the shows back in the day, they brought in a young kid when the ratings dipped. So now turns to the real question, Did her husband (the Teacher) kill Rosie Larsen. or Did Crissy Seaver kill her. And why hasn't Alan Thicke guest starred on this show?