The (New Orleans) Times-Picayune reported Tuesday prosecutors said the mother of Todd Singleton, the group's alleged ringleader, deleted the invite-only Facebook page "Day Zero," on which the boys purportedly planned the attack at Lakeshore High School, then destroyed her son's computer.
The trial of Singleton, Jacob Keller and Daniel Hopkins, all 15, was to begin next week. They are charged with conspiracy to commit terrorizing and solicitation for murder.
Judge Mary Devereux granted a delay requested by prosecutors.
The St. Tammany Parish Sheriff's Office, which has issued subpoenas to Facebook, is working with federal agencies and authorities in California to serve a search warrant to the social media site, based in Palo Alto, Calif., the Times-Picayune said.
The boys allegedly plotted to attack during the first day of school on the Facebook page, accessible only to people invited to join the group.
Prosecutors are relying on statements the boys gave to police, an exchange of text messages, online messages between the boys and the missing Facebook page.
Police said after their arrests the boys had a detailed plan to shoot at least one student, a staff member and anyone who tried to stop them, then commit suicide.
Detective Brian Beech testified at a hearing Friday Singleton had told him Aug. 1 the boys planned to steal guns from a safe, shoot one specific student, the school resources officer and as many others as they could. Beech said he took notes but did not record the interview.