The irrigation canals of Leeton were closed and emptied to enable a search, the cost of this to the community is huge and ongoing, the helicopters, the travel and accommodation of Homicide officers to Leeton, the door to door investigation, the counsellors for the kids of the school, the immeasurable cost to Stephanie's parents and fiancé, to the teacher colleagues of the school...
And if I might hark back to the claim that Vincent was at the school hoping for the 12 yr old he was stalking to turn up, this insight into Vincent could only have come from Marcus, .. I cannot see Vincent admitting to this creepy failure, he and Marcus had to have had a conversation about this child, and Marcus, not Vincent would have passed it onto the detectives at some stage.
For this alone Marcus should get 10 years, for aiding and abetting in the procurement and planning of abduction for nefarious purposes , a small female child. .. for withholding that information from authorities , add on an extra 5 years.