Jesse Marcel was an intelligence officer of the 509th Bombardment Group at Roswell Army Air Field and was tasked with investigating the 1947 Roswell crash

Marcel's grandchildren are now telling his story decades after the event

They say he determined the wreckage was 'not made by human hands'

Marcel said there were beams with 'alien writing' etched across

However, the US government said the debris was remains of a weather balloon 

Marcel's grandchildren have been holding onto his journal for 15 years

They say it could unravel the 'true story' to what really happened in Roswell