Colin Gray, whose 14-year-old son is charged with murdering two students and two teachers at a Georgia high school last month, himself faces 29 criminal charges that could send him to prison for the rest of his life. The case is part of a troubling trend in which prosecutors seek to spread the blame for school shootings by criminalizing parental failures. Judging from the allegations against him, Gray is no one’s idea of a model parent. Prosecutors say he failed to securely store the rifle used in the September 4 attack at Apalachee High School in Winder, a weapon he bought his son, Colt, as a…