The sinking of Convoy PQ17 in July 1942 was the inspiration for "Bad Blood." Of the 37 ships that began the journey from Iceland to Russia, only 11 got through. The rest were sunk by the German navy. 153 merchant marines were lost.
The murder weapon is a veterinary trocar. Cattle can develop bloat, trapped gas in their stomachs, severe enough to kill the animal. A trocar is punched through the animal's side, into its stomach, and the high pressure gas is released. Rather like stabbing a car tire.