Satch considered retiring on Frequency Season 1 Episode 7, but that was before more evidence than ever dropped into their laps about the Nightingale Killer. Onward!
On Frequency Season 1 Episode 4 Frank and Raimy each try to reach a girl who had a run in with the Nightingale Killer, but got attached to the fame associated with it.
Raimi and Frank have their first real suspect for the Nightingale killer on Frequency Season 1 Episode 2, but with every avenue they cover, things change.
On Frequency Season 1 Episode 1, on Raimy's 28th birthday, she solves the mystery behind her father's abandonment 20 years earlier after she talks to him from beyond.
Frank: You're a cop? Get outta here. So you're telling me in 20 years I'm going to be on teh job with my daughter? Raimy: No. Frank: What? I'm retired? Raimy: You're dead. You die tomorrow.