Chris Kyle's widow broke down in tears when describing text message which made her worried about her husband

The widow of Chris Kyle, the 'American Sniper', broke down in tears when she described sending her husband a text message he didn't respond to on the day he died.

Kyle, a former US Navy SEAL, was shot and killed along with friend Chad Littlefield on 2 February, 2013 at the age of 38 by ex-marine Eddie Ray Routh.

He and Littlefield were shot a combined total of 13 times with guns Kyle had given to Routh at a shooting range the three of them had travelled to.

They had taken Routh to the shooting range as part of an attempt to help him with PTSD - the ex-marine had served in Iraq and helped the aftermath of the Haiti earthquake, with him having been in and out of veteran's hospital before his mother had asked Kyle if he could help with her son's trauma.

Kyle, who had himself suffered from PTSD, sponsored outings for former soldiers where veterans could go hunting and shooting together.

On the day he died a number of text messages sent by Kyle and others around him shed light on the events and moods of the people involved.

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A message from Kyle to Littlefield sent as they drove up to the shooting range read: "This dude is straight up nuts," which was met with a response of: "He's right behind me, watch my six."

Routh later told police when arrested that the two men 'wouldn't talk to me' and a forensic psychologist concluded that he believed Kyle and Littlefield were planning on killing him.

At Routh's trial, Kyle's widow Taya was emotional as she recounted her last contact with her husband - a phone call where she said she knew something was wrong as she could tell Chris was irritated.

She then told the court that she later tried to send him a text message which received no response, and shortly afterwards a police officer showed up to her house to tell her that her husband was dead.

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Routh testified that he had opened fire on the pair, shooting Littlefield seven times in the back, shoulder, head and hands before shooting Kyle six times in the head, chest, shoulder and right arm.

The former Navy SEAL was recognised as the deadliest sniper in US history, claiming 255 kills and having 160 of them confirmed.

He was the subject of the 2014 Clint Eastwood film American Sniper, with Bradley Cooper taking on the leading role.

Before he died, Kyle had said in an interview that he had not regretted any of his kills and agreed with the statement that it was a case of 'you kill them or they kill other Americans'.