Two men found guilty of cutting down famous Sycamore Gap tree

Interesting question. I remember they were caught fairly quickly after it happened. I don’t know much about UK surveillance or device searching laws.

Edit: some other suspects were arrested before these two, then released. I wonder if they testified?

Another article mentions this:

Police analyst Amy Sutherland told the court the video was in the download section of Graham's phone, which was taken from his jacket pocket.

If it was unlocked perhaps the police were just able to open it and view the file. Here in the US the main obstacle is the lock on the phone which usually police can’t get past, though maybe there’s a secret way for high profile cases, I couldn’t say.