This dude is straight-up nuts.

What Chris Kyle, who story is told in American Sniper, texted to a friend about the man on trial for killing him. A lawyer for Eddie Ray Routh said in opening statements of the man’s murder trial that Routh’s insanity was so evident that Kyle and his friend Chad Littlefield exchanged texts expressing alarm as the three rode together in February 2013 to a Texas shooting range.

“He’s (sitting) right behind me, watch my six,” Littlefield texted back, using a military reference for watching one’s back.

But a prosecutor said Routh still knew right from wrong, even with a history of mental illness.

The first day of the highly anticipated trial also included sometimes tearful testimony from Kyle’s widow, who spoke about her husband’s passion for helping veterans, gun safety and opposition to mixing alcohol with gun use.

The case has drawn intense interest, largely because of Kyle’s memoir about being a sniper who served four tours in Iraq. The Oscar-nominated film based on the book has grossed nearly $300 million.