Former US Marine Eddie Routh has been sentenced to life in prison for the murders of Chris Kyle, who inspired Clint Eastwood’s box-office hit “American Sniper”, and Chad Littlefield two years ago.

A jury of 10 women and two men Tuesday declared Routh to be guilty at the end of a trial that lasted two weeks in Stephenville, Texas, during which the former Marine tried to avoid conviction by claiming that he suffered from dementia.

Routh was given an automatic life sentence on being found guilty, as the prosecution did not seek the death penalty.

Routh shot dead Kyle and Littlefield Feb 2, 2013, at a Texas shooting range when they were trying to help him with the problems he suffered after serving in Iraq and Haiti.

The defence unsuccessfully tried to establish that Routh committed the crimes under schizophrenia-related psychotic delirium and post-traumatic stress that he suffered from his military service, and was not aware of what he was doing.

The trial generated huge media interest as it coincided with the success of “American Sniper”, directed by Eastwood and which is based on Kyle’s memoir of his experiences.

Kyle served in the Navy SEALS, the most elite unit of the US military during the US occupation of Iraq, and was known as the most lethal sniper in the country’s history, with 160 confirmed kills to his name.