Nothing could have been done to prevent the death of Daily Mirror defence correspondent Rupert Hamer, who died in a blast in Afghanistan in January last year, the Press Association reports from an inquest into his death.
An inquest in Trowbridge, Wiltshire heard that he died despite wearing full standard issue body armour.
A US Marine was also killed and Sunday Mirror photographer Philip Coburn, who was sitting next to Mr Hamer, was seriously injured.
Recording a verdict of unlawful killing, David Ridley, Wiltshire and Swindon Coroner, said: “No matter how much training was given, I don’t think it would have changed the outcome.
“This was not an act of war. It was a cold-blooded killing. The purpose of the device was to maim and kill American service personnel.
In the days after his death the Mirror paid tribute to Hamer, who had worked for the title for 12 years.