Leon's father-in-law told AP he had no immediate comment
"There should be more than just a two-sentence apology," Leon's sister-in-law Amber Lane told The Denver Post. "I thank somebody for taking accountability for the error, however it doesn't bring Nate back."
The court officials vowed to review their procedures to ensure the error isn't repeated.
"The Colorado Department of Corrections values its long-standing partnership with the 11th Judicial District and the district attorney's office to maintain order at the prisons in Canon City. We commend both the 11th Judicial District and the DOC for reviewing their own internal processes and procedures," Gov. John Hickenlooper's spokeswoman Megan Castle said in a written statement.
The attack that led to the plea deal took place in 2006. According to prison and court records, Ebel slipped out of his handcuffs while being transferred from a cell and punched a prison officer in the face. He bloodied the officer's nose and finger, and threatened to kill the officer's family.
"If Mr. Ebel was prosecuted for an assault on an officer, it had to be pretty severe, because in the course of day-to-day work, correctional officers are regularly assaulted or threatened," said Pueblo County Commissioner Buffie McFadyen, who is executive director of the correctional officer group Corrections U.S.A.
"It sounds like a horrific oversight," she said of the mistake that led to Ebel's release this year. "It's a tragic clerical error."
Ebel spent much of his time behind bars in solitary confinement and had a long record of disciplinary violations. Records show he joined a white supremacist prison gang.
Ebel's early release was just the latest twist in a case full of painful ironies. His father is friends with Hickenlooper and had testified before the Colorado Legislature about the damage solitary confinement did to his son. Clements was worried about that very issue.
Hickenlooper raised the case with Clements when the governor hired him to come to Colorado in 2011. The Democratic governor said he never mentioned Ebel's name and the inmate received no special treatment.