Tragedy struck Dog the Bounty Hunter‘s family last year when his 13-year-old step-grandson Anthony was shot and killed … and now we’ve learned Dog’s stepson Gregory Zecca has been arrested for the fatal accident.

According to Florida’s Collier County Sheriff’s Office … Zecca was determined to have been under the influence of alcohol while he was handling the firearm last July. Law enforcement obtained an arrest warrant charging Zecca with aggravated manslaughter of a child with a firearm and using a firearm while under the influence.

Sheriff Kevin Rambosk said in a statement … “This was a heartbreaking and preventable tragedy. Our detectives conducted an exhaustive and thorough investigation, examining every element of what happened through witness statements, forensic testing, subpoenas, search warrants, and more. I commend their hard work and professionalism in uncovering the facts in an incredibly difficult case.”

According to the investigation, Gregory was drinking for several hours before sitting down to watch a UFC fight on TV with his son at a friend’s house. At the friend’s house, Gregory continued to drink and got high on marijuana, authorities say.

Law enforcement says Gregory “repeatedly handled a firearm in the child’s presence, practicing drawing it from his waistband and dry-firing. The firearm had initially been rendered safe by removing the magazine and clearing a live round from the chamber.”

But at some point, authorities say, “the magazine was reinserted and a round chambered, and Gregory discharged a single shot, fatally striking the child.”

According to Sheriff Rambosk, “This case underscores that devastating tragedy that can result from mixing firearms, alcohol and drugs. Our hearts are with everyone affected by this loss.”

Gregory’s aggravated manslaughter charge carries a potential penalty of life in prison.