sup3rc0w, sucks about your local ratbag dude. Get some CCTV, you can pick it up pretty cheap from the catalogue place and other such establishments. Of course this would require you to stick your new bike in the shed as bait... so perhaps try with a different bike 
Is the shed in your back garden? Surely they'd have to have line of sight into your back garden to see the bike is in the shed... else how would they know it's not in the house?
OR, they just periodically bust into your garden every other night, check out the shed, and got lucky that second time
Either way i'd seriously think about getting that CCTV. The idea that someone is in and out of my property would really give me the willies. Sure they only nick bikes, but what if one day their balls dropped and they decided they had the minerals to take it further... :/

Is the shed in your back garden? Surely they'd have to have line of sight into your back garden to see the bike is in the shed... else how would they know it's not in the house?
OR, they just periodically bust into your garden every other night, check out the shed, and got lucky that second time

Either way i'd seriously think about getting that CCTV. The idea that someone is in and out of my property would really give me the willies. Sure they only nick bikes, but what if one day their balls dropped and they decided they had the minerals to take it further... :/