WDRB-TV, Louisville, Ky., reported an attorney for Michael Carneal argued in the 6th U.S. Circuit Court of Appeals in Cincinnati that their client's appeal in the 1997 triple slayings at Heath High School in Paducah, Ky., was timely and should be allowed. The Kentucky News Network reported Tuesday a judge had ruled he waited too long to withdraw his plea.
Carneal has been diagnosed with schizophrenia and his attorney argues he wasn't mentally competent to plead guilty at the time, the TV station said.
The appellate court's ruling could take months.
Carneal, now 29 and serving a life sentence at the Kentucky State Reformatory, opened fire on a prayer group at the school on Dec. 1, 1997. Besides the three students were killed, five were wounded.
Carneal once told The (Louisville) Courier-Journal he did it because he had been picked on in school and believed "nobody loved me and nobody cared." He said he knew he would go to prison.
"But in my mind, I was leaving everything behind," he said. "I perceived my life as miserable."
Notable deaths of 2014 [PHOTOS]