EASTLAND — An attorney for Eddie Ray Routh, who in February 2013 killed 'American Sniper' Chris Kyle and Chad Littlefield, argued in an appeal before the 11th Court of Appeals Thursday that his client suffered from schizophrenia and did not understand the consequences of his actions when he shot both men.

In his initial trial, Routh's defense argued he was schizophrenic and suffered from post-traumatic stress syndrome. A jury in Stephenville rejected that insanity plea, and on Feb. 24, 2015, convicted Routh of the murders of Littlefield, 35, and Kyle, 38.

Routh was sentenced to prison without parole. In his appeal Thursday, attorney J. Warren St. John of Fort Worth argued Routh did not know his conduct was wrong when he shot the decorated Navy SEAL and his friend.

St. John told justices that the case had significant national and international interest based on the 'sad consequences' of the Feb. 2, 2013, shooting and said that there was no doubt that Routh took Kyle and Littlefield's lives. Kyle's military career is highlighted in his autobiography 'American Sniper,' made into a movie of the same name.

St. John argued that evidence indicated Routh was insane at the time of the offense, based on expert testimony and comments from others, including Routh's girlfriend, uncle and sister — the latter two family members he visited immediately after the shooting.

On the day of the murder, while traveling to a gun range with Kyle and Littlefield, St. John said Routh, who earlier had what the defense brief characterized as 'several psychotic episodes' with his girlfriend, believed that Kyle and Littlefield 'were trying to kill him.'

According to court documents, on the day of the killings Kyle texted Littlefield that Routh was 'straight up nuts,' while Littlefield texted back 'watch my six,' meaning 'watch my back.'

Following the shooting, Routh fled in Kyle's truck, visited family members and said 'bizarre' things, including telling his sister that he 'committed a murder' and his uncle that he was driving a 'dead man's truck.'

In a second reason to overturn the case, St. John argued that Routh's mental state meant he should not have been interviewed by Texas Ranger Danny Briley.

St. John's brief states that the Ranger asked Routh if he wanted to speak to him, but Routh never stated he would and was 'in a psychotic state.'

Routh 'has an absolute right to remain silent, and that (interview) was used against him in the trial,' St. John said Thursday, while admitting the evidence was a 'double-edged sword' as it also helped show a snapshot of his client's mental state.

M. Alan Nash, 266th district attorney in Erath County, said that 'the record and the law support the jury's rejection of (an) insanity defense.' 'The jury had the exclusive purview and ability and the right to disbelieve or disagree with the conclusions reached by the expert testimony given,' Nash said.

In its legal brief, the prosecution maintained that Routh did not meet the definition of insanity in the state of Texas and was suffering symptoms of a mental disorder or disease 'as a result of drugs and alcohol.'

Addressing the diagnosis of schizophrenia, Nash's brief also stated that one of the prosecution's own expert witnesses, Dr. Randall Price, stated his opinion was 'that Mr. Routh knew what he did was wrong.'

Price also said he felt that Routh's symptoms before, during and immediately following the crime were 'cannabis-induced' and that he was 'instantly remorseful'' following the shootings.

Briley's videotaped interview was 'the most temporally proximate indication' of Routh's state of mind at the time the offense occurred, Nash said Thursday, and it became a core issue because 'the overwhelming evidence of his guilt' while showing his mental condition at the time.

Even if an error had occurred in admitting Briley's statements, Routh's conduct during and after the shootings indicated overwhelming evidence, Nash argued, that he murdered Kyle and Littlefield.

Inadmissible evidence can be rendered harmless if other evidence of the defendant's guilt is overwhelming, Nash said, arguing the state 'came back with compelling testimony' from two experts, as well as testimony regarding Routh's actions and demeanor before, during and after the crime.

Nash's brief says that 'evidence of (the) appellant's guilt was so overwhelming, independent of the statements, that such error did not substantially affect the jury's finding of guilt.'

The trio of justices who heard the case will render a decision in several months.