WASHINGTON -- Floyd Lee Corkins, who has already pleaded guilty to shooting a security guard at the D.C. headquarters of the conservative Family Research Council in August of last year, should spend 11.5 years in prison, a federal public defender argued Tuesday.

Corkins was carrying a handgun, ammunition and 15 Chick-fil-A sandwiches when he shot Family Research Council employee Leo Johnson in the arm on Aug. 15, 2012. In a 13-page filing with the D.C. federal trial court, Assistant Federal Public Defender David Bos argued that Corkins should serve 138 months in prison for his "nearly unimaginable" crime. Federal prosecutors are seeking 45 years for the 29-year-old Virginia man, whose sentencing has been delayed because of sequestration's impact of federal public defenders.

If Corkins "were unrepentant or unremorseful for his conduct, and not suffering from a mental illness at the time he committed the offenses, a severe sentence might indeed be warranted in this case," Bos stated.

But Corkins was "experiencing auditory hallucinations" and had "thoughts of killing his parents and conservative right-wing Christians" in the months leading up to his crime, his lawyer argued. The day before the shooting took place, he missed his monthly shot of an anti-depressant drug.

Corkins is scheduled to be sentenced by Chief U.S. District Judge Richard W. Roberts next Thursday, Sept. 19.