The father of a 14-year-old responsible for a September school shooting in Georgia pleaded not guilty to charges of second-degree murder, involuntary manslaughter and cruelty to children on Thursday, multiple outlets report. Colin Gray, 54, is being held responsible for the deaths of four people after his son, Colt Gray, killed Richard Aspinwall and Cristina Irimie, both instructors at Apalachee High School, and students Mason Schermerhorn and Christian Angulo in a premeditated mass shooting.  Colt Gray has been charged with four counts of felony murder. Authorities said the boy had pictures of the Parkland school shooter in his room months before his attack and detailed plans for the shooting in a notebook, according to reports from CBS.  Colin was arrested and placed at Barrow County jail shortly after the incident. A few days later, he requested to be separated from the inmate population due to the threat of violence from other inmates. “[M]ost notably social media has led to a nonstop barrage of information being transmitted to the public leading to an incalculable number of threats against the Defendant and calling for both harm and violence to befall the Defendant, and in some cases, even calling for the death of the Defendant,” said his attorneys Jimmy Berry and Brian Hobbs. “It is certain that those feelings of anger and retribution manifested in the collective psyche, of both the public and the community at large, are not also represented in the individuals currently incarcerated,” they added in their motion to the Superior Court of Barrow County. The FBI previously revealed Gray had been investigated for threats after the agency received “several anonymous tips” about the students' online comments.  Colin Gray is not the first parent to be charged in connection with their child's mass shooting. Earlier this year, James and Jennifer Crumbley, the parents of school shooter Ethan Crumbley, became the first parents in the U.S. to be charged and sentenced after their child carried out a mass shooting.