The shootings near Annecy in the French Alps which left two young girls without their parents and grandmother made headlines around the globe last year, and now, for ther first time, Channel 4 is looking back at the murders of the British family and French cyclist Sylvain Mollier. Nobody knows what happened that day, or indeed why, but conspiracy theories are plentiful and speculation is rife. Were they spies? Was religious extremism to blame? We may never know, but the documentary makers are determined to see what they can find out...