We have a similar problem at our work, with a bunch of scallys - who have definitely been responsible for thefts, they are kids, so they are hard to tackle physically, we have a small but determind group of colleagues who keep watch when they can, we've gone down the path of warning other riders to lock up their bikes properly (signs etc) taking photos of them (they hate that) and getting the local police involved - they eventually took interest - but it took some badgering of the local estate landlords before, this is also one of the reasons I got my Xena alarm lock so I could make the little fuckers ears bleed and draw as much attention to them as possible.
We have a similar problem at our work, with a bunch of scallys - who have definitely been responsible for thefts, they are kids, so they are hard to tackle physically, we have a small but determind group of colleagues who keep watch when they can, we've gone down the path of warning other riders to lock up their bikes properly (signs etc) taking photos of them (they hate that) and getting the local police involved - they eventually took interest - but it took some badgering of the local estate landlords before, this is also one of the reasons I got my Xena alarm lock so I could make the little fuckers ears bleed and draw as much attention to them as possible.