James Holmes' attorneys, while admitting it's a formidable request, allege information leaked to Fox news concerning the contents of a notebook Holmes mailed to his psychiatrist violated a judge's gag order, The Denver Post reported Tuesday.
The defense's plans open up another battlefront as both sides prepare for a Jan. 7 preliminary hearing during which investigators are expected to discuss never-before-told details about the July 20 shootings in which 12 died and at least 58 were at the Century Aurora 16 theater during a midnight screening of the latest movie in the Batman franchise, the Post said.
Laws shield reporters from having to reveal sources and overcoming them is difficult.
Defense attorney Daniel King acknowledged the outcome of the promised subpoena was uncertain. During a hearing Monday, 14 law enforcement officials testified they never spoke to the media about the Holmes case.
"It appears to me," King said after Monday's hearing, "we are going to be executing an out-of-state subpoena -- or attempting to do so."
A Fox News spokeswoman told the Post the news organization would evaluate the subpoena once it is served.
The hearing in Centennial was Holmes' first appearance in court since he was taken to a hospital last month after ramming his head into an Arapahoe County jail cell wall.
The next hearing is Jan. 2, when both sides are expected to confirm whether they are ready to proceed to the preliminary hearing.