I think there's nothing inherently wrong with taking a close look at this. No doubt in my mind he gets cleared.
Edit: I did a tiny bit of research into this. So apparently the UK's law enforcement system is very different from the US, which is what I'm familiar with. In the US, they typically arrest you if they are fairly confident you did the thing you are being accused of. In the UK, it seems like they tend to arrest people just to start the investigation. So it's very possible this was just so they could look closer into it.