What a Scam Detective Do?

Crippen and Ethel have no idea that number one, people know they are on board. The man on the case is taking an even faster boat to meet them in Canada because he's gotten this information. In this time period to receive information on a criminal or a suspected criminal, as you would say, there's nothing that would have stopped him from walking off that boat and disappearing. Even if people were suspicious, they couldn't have stopped him, only the police could do it.