Wrongful arrest as MagicDude4Eva said.
Cops will simply provide evidence backing their point of view at the time. AFAIK it's only wrongful arrest if they were inept and/or intentionally arrested the bloke knowing he was innocent. I guess at the time evidence pointed to him being the guilty party and subsequent investigation proved that premise to be false, or the case requires further investigation before the prosecution is happy to file official charges. I guess they could argue that they in fact did their job as required of them. Hell, they're trying to prove that a terrorist is on the loose.
Just because the prosecution has decided not to file charges at this point doesn't necessarily imply that he was wrongfully arrested. IMO at least. Someone with a better law background than myself can confirm or tell me I'm talking kark...