The mother of the teenager suspected of killing four people during last week’s shooting at a Georgia high school has apologized to the victims’ families in an open letter while insisting her son “is not a monster.”

“To the parents and families of those affected by the tragic events at Apalachee High School, I want to say that I am so sorry from the bottom of my heart,” Marcee Gray, the mother of Colt Gray, wrote in the letter, which she provided first to CNN.

The letter comes one week after the shooting, which authorities allege was carried out by Colt, leaving two teachers and two students dead at Apalachee High School in Winder, Georgia. Seven others were wounded by being shot, and two others suffered other injuries, authorities said.

“If I could take the place of Mason and Christian, I would without a second thought,” Marcee Gray wrote, referring to the two 14-year-olds killed in the mass shooting, later adding her “heart breaks for the 2 teachers who gave their lives while in the service of teaching and protecting our children.”

“We are all in a living nightmare right now, and I will personally never forgive myself for what has happened,” she wrote. “My son Colt is not a monster. He is my oldest baby. He is quiet, thoughtful, caring, funny, and extremely intelligent. Please pray for him and the rest of our family, as I am praying for all of you every moment of every day.”

Marcee Gray received a text the morning of the shooting from her son that read, “I’m sorry, mom,” the suspect’s grandfather previously told CNN. It was concerning enough that Marcee Gray called the school to warn of an “extreme emergency” at 9:50 a.m., about 30 minutes before police responded to the school for a shooting, according to call logs and a text exchange between Marcee Gray and her sister, who provided them to CNN.

This is a developing story and will be updated.