As I understand it, PA asked PF to join the search. But because there was still an active police investigation going on, PF could only search the area with their permission, and only where they told him to search.
The other night I performed an Advanced Twitter search to track the history of PF's involvement. It went:-
1. PF starts popping up on TV somewhere, saying that he's got amazing sonar equioment, and that even if the police have the same equipment they might fail, because 'it's only as good as the person using it; and I'm the best'.
2. The Twitterverse starts tweeting 'this search needs PF'.
3. There are tweets saying 'I'm glad MWT suggested to PA that he contacts you, Peter' (during this time PF is saying he can do it for free because it so happens his team have some days spare)
4. PF and his merry red helicopter etc. turns up at the location.
So my belief is that PA asked LP, and LP said 'if he's doing it for free, and it's another resource, yes, great'. But he wasn't there to determine strategy or to be privy to the investigation itself. He was literally told where on the river his searching would be of assistance.