Dennis Dickey, an off-duty Border Patrol agent, was celebrating his wife’s pregnancy at a party near Green Valley, Ariz., on April 23, 2017, his attorney told the Arizona Daily Star on Friday. In preparation, he had filled a target with colored powder. When it exploded, it would reveal their future child’s sex: pink for a girl or blue for a boy.

The target also contained Tannerite, a legal but highly explosive substance, U.S. Forest Service special agent Brent Robinson wrote in an affidavit filed in federal court on Sept. 20. When Dickey, now 37, fired his rifle at the target, the ensuing explosion sparked a fire that quickly spread through the dry brush, spurred on by unusually high winds and lower-than-average rainfall. By the time it was fully contained over a week later, the fire had done $8 million worth of damage.