The NTSB investigation reveals the helicopter's fuel was contaminated with water. The report says Vinuti kept aviation fuel in a barrel on his property, and that he would pump fuel from those barrels into 5-gallon plastic cans, which he used to fuel the helicopter. Investigators tested and found "one of the cans contained a mixture of about 50% aviation fuel and 50% water, and another contained a mixture of about 85% aviation fuel and 15% water."
Read more: http://www.good4utah.com/news/ntsb-reveals-contaminated-fuel-cause-for-last-years-deadly-helicopter-crash-near-green-river