Question or Plot Hole: Episode 5 - The Boat .... (**Spoilers**)

In episode 5 the police arrive to arrest a suspect who tries to escape by running on to the cross channel ferry. We see the ferry depart, with suspect and police on board, and once it's out to sea Sandra finds the body of the murdered suspect on the back deck.

Surely that whole scene only makes sense if Maisonneuve had turned out to be killer? For it to have been Damien he'd of had to know the police were planning to visit the suspect and have followed the suspect & police onto the ship (ignoring the fact he would of needed a ticket for that!)

As the ship was at sea when the killer struck Maisonneuve and Co could of simply locked it down and gone through each passenger one-by-one until they found, and indeed recognised, Damien. (Or just arrested the only person on board without a ticket ...)

I think I must have missed something in the lead up to this scene - or - the writers had intended Maisonneuve to be the killer, but changed their minds towards the end of the series! (I think a lot of the series makes more sense if he was involved all along.)