"American Sniper" may be experiencing a great deal of success at the box office, but the attorney of Chris Kyle's accused killer says the success may have a negative effect on his client's trial.

Kyle and his friend, Chad Littlefield, were allegedly killed on Feb. 2, 2013, four years after he left the military, on a Texas gun range while helping former Marine Eddie Ray Routh, then 25, recover from post-traumatic stress disorder, according to People Magazine.

J. Warren St. John, Routh's attorney, says his client "will plead not guilty by reason of insanity," and that it may be difficult for the jury to remain impartial for the trial, which is scheduled for Feb. 11, based on how well the film based on Kyle is doing.

"The film will be an issue," St. John says. "I think any case with significant publicity has an issue with picking a jury. I've had them in the past, and anything that has significant national attention makes it hard to pick a jury."

"American Sniper," directed by Clint Eastwood and starring Bradley Cooper as Kyle, has earned six Oscar nominations and made over $110 million in four weeks, Fox News reported.

Prosecutors have said that they are not seeking a death penalty in Routh's case. A judge issued a gag order two years ago that required attorneys and family members to refrain from talking to the media about specific details about the case due to the "unusually emotional nature of the issues involved in the case" and the "extensive local and national media coverage this case has already generated."

St. John isn't the only one worried about the outcome of Routh's trial, as Houston criminal defense attorney George Parnham, who represented Andrea Yates (who was convicted of drowning her five children before being found not guilty by reason of insanity), said the jury could be influenced by the movie, People Magazine reported.

"It's going to be very difficult for him to get a fair trial, not only because of the movie, but because of the media surrounding the movie," Parnham said. "Mr. Kyle is a hero in many people's eyes. Due to the fact that this movie has gained intense public attention, it's doubtful that a fair jury can be selected anywhere."