The order of incompetency was issued for Benjamin Bishop during a hearing Wednesday after three doctors evaluated him separately in November, May and June, the Tampa Bay (Fla.) Times reported.
One doctor deemed him competent, while the other two disagreed.
"He's not able to communicate with lawyers and doesn't know what's going on," Bruce Bartlett, chief assistant state attorney for the Pinellas-Pasco circuit, said.
Bishop will be sent to a mental health facility for treatment, and doctors will send the court updates on his condition.
"If at some point they feel like he has returned to a state where he is competent, then they would send him back here for further proceeding," Bartlett said.
Bishop has pleaded not guilty to two counts of first-degree murder.
Police told the Times that he confessed to fatally shooting his mother, Imari Shibata, and her boyfriend, Kelley Allen, on Oct. 28 while the victims were in bed.
A psychiatrist had diagnosed Bishop with schizophrenia before the killings.