Complex sentence: Two sets of footprints were then discovered at the back of the shop; these tracks appeared to belong to the killers as they contained both blood and sawdust from carpentry work done inside earlier in the day.
Split into simpler sentences: Two sets of footprints were then discovered at the back of the shop. These appeared to belong to the killers, as they contained both blood and sawdust from carpentry work done inside earlier in the day.