Military veteran Eddie Ray Routh's concrete motive for killing "American Sniper" Chris Kyle and Chad Littlefield on February 2, 2013 at a shooting range is still undetermined even as the trial and investigation continue.

The murder trial has been going on for eight days now but there still is no logical answer as to why Routh killed the two men who was just trying to help him. Routh has been giving incoherent explanations as to why he took the lives of the two men.

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According to the attorney of the former Marine, Routh has been suffering from paranoia, psychosis, and schizophrenia. On the other hand, prosecutors handling the case counter that the suspect might be suffering from personality disorder but noted that he is not insane.

Routh's attorneys also suggested that the firearms lying near Routh and the paranoia during the car ride triggered the killing.

Also, his defense attorney Tim Moore suggested that Routhe felt he had to take their lives because he felt like he was in danger. When Kyle and Littlefield started to shoot pistols at the range Routhe though that it was a showdown and that made him angry.

Dr. Randall Price, a forensic psychologist for the prosecution's medical expert, testified that Routh's heavy use of marijuana caused a substance-induced psychotic disorder. Dr. Mitchell Dunn, a forensic psychiatrist, believes that the psychosis was not at all substance-induced as he thinks Routh is suffering from a severe mental disease that caused him not to determine if what he was doing at that time was right or wrong.

According to Dunn, proof that Routh is having mental problems is when a video from the police car was reviewed after his arrest as he noted that the suspect was complaining of confusion. He reportedly told the officer that he has been so "paranoid-schizophrenic all day" and that he did not know what to think of and he is not sure if he is sane or insane.

Gene Cole, an officer in the Erath County Jail where Routh is being held, recently testified that he heard Routh talk about the killing four months after the incident. Routh reportedly said that he shot them because they would not talk to him when they were on their way to the shooting range.

"I was just riding in the back seat of the truck and nobody would talk to me. They were just taking me to the range so I shot them," Routh allegedly said. "I feel bad about it, but they wouldn't talk to me. I'm sure they've forgiven me."

A month after the 2013 incident, Routh had a phone interview with magazine writer Nicholas Schmidle and said that he was annoyed with Kyle and Littlefield and that he did not trust the two upon meeting them.

Kyle had ensed that there was tension when they had the 90-minute drive that he even texted Littlefield that he felt Routh was "straight up nuts."

Kyle was shot four times in the back and once in the face while Littlefield was shot five times in the back. The trial is set to continue on Tuesday and that closing arguments are expected to be stated within the week.

TagsAmerican Sniper, Chris Kyle, Chad Littlefield, Eddie Ray Routh, military veteran