By Rachel Leigh| April 25, 2013 at 3:34 PM EST - Updated July 11 at 3:51 PM
PORT ST. LUCIE, FL (WFLX) - Tyler Hadley, the St. Lucie County teen accused of bludgeoning his parents to death, has filed a notice declaring he will rely on an insanity plea in his upcoming trial.
Public defender Diamond R. Litty announced the plea Thursday at noon which states the defense expects to prove that at the time of the incident, Hadley was "laboring under a mental disease, infirmity or defect, to wit: depression".
The filing also states Hadley was involuntarily intoxicated. The defense expects to call Dr. Kathleen Heide and Dr. Wade Myers, to prove insanity.
Hadley, who is 18 now, was 17 years old on July 16, 2011, when he allegedly beat his parents, Mary Jo Hadley, 47, and Blake Hadley, 54, to death with a hammer at the family's home in the 300 block of Northeast Granduer Avenue in Port St. Lucie and then sent out invitations via Facebook for a party at the house.
In an apparent reference to an insanity plea, Hadley wrote in a Nov. 29 letter from the St. Lucie County Jail to Michael Mandell, his best friend and the prosecution's key witness: "We do have a very strong defense and could beat the (first-degree murder) charge if we go to trial. I could be lookin' at 20-40 years in the pen, but at least I'll get out. If I plead insanity and go to a state hospital, I'm lookin' at 10 or 15 years. That's what I pray for."
Mandell told said Hadley took three pills of the psychoactive drug, commonly known as ecstasy, before the homicides: "He said he couldn't do it sober."
If convicted of first-degree murder, Hadley faces a mandatory sentence of life in prison without the possibility of parole. Because of his age at the time of the homicides, he cannot be executed.
Scripps Treasure Coast Newspapers contrinbuted to this report.