The victim managed to struggle free and two schoolboys heard her screams. They tracked Walsh and alerted nearby allotment holders, who detained him until police arrived and arrested him.
Don't mess with middle-aged men bearing shovels.
Or (to be less flippant about what is really a serious matter) communities make us all safer. If two resourceful schoolboys asked me for help in detaining a rapist I'd probably be too scared to act alone. But if they asked me and a bunch of other people I knew and trusted, I'd be glad to help. That might be my neighbours, my colleagues, or my fellow allotmenteers.