Arizona rancher George Alan Kelly, who already faces a first-degree murder charge for the shooting death of a Mexican man, now also faces two charges of aggravated assault Tuesday, just one day before his scheduled preliminary hearing.

The additional counts filed in Santa Cruz County each say Kelly "using a rifle, a deadly weapon or dangerous instrument, intentionally did place [unnamed person], in reasonable apprehension of imminent physical injury." But this filing like others from the government so far fails to specify how or why authorities believe Kelly is the responsible party.

In his own court filing from earlier this month, Kelly — who remains held on $1 million bond — says he’s an innocent man. He admits to firing his rifle in the air in late January to scare off armed drug traffickers. Those men, he says, are the ones responsible for the shooting death of a Mexican national found shot to death on Kelly’s borderland property outside Nogales.  

Kelly, 73, is charged with first-degree, premeditated murder in the Jan. 30 shooting of a man whom authorities believe to be 48-year-old Gabriel Cuen-Butimea, based on the Mexican voter registration card he carried. The rancher had completed chores on his ranch near Kino Springs earlier that day and came to his house to have lunch with his wife when he heard a single gunshot as they ate, Kelly’s court-appointed attorney, Brenna Larkin, wrote in a court filing previously obtained by Fox News Digital.

ARIZONA RANCHER HELD ON $1M BOND FIRED ‘WARNING SHOTS’ ARMED MEN ‘POINTED AK-47 RIGHT AT HIM,’ DEFENSE CLAIMS 

Kelly saw his horse, who is old, running away scared at full speed, the filing says. 

Arizona border shooting death

George Alan Kelly, 73, is being held on $1 million bond in the fatal shooting last month of a man identified as a Mexican national on his property.  (Santa Cruz County Sheriff's Office via AP)

"Finally, he saw a group of men moving through the trees around his home. They were armed with AK-47 rifles, dressed in khakis and camouflaged clothing and carrying large backpacks," Larkin wrote. "None of them were known to him. He had not given any of them permission to come onto his land.

Because he was "understandably concerned and reasonably feared for his safety, his wife’s safety, and his animals’ safety," Kelly called the U.S. Border Patrol ranch liaison, specifically assigned to aid people living on borderlands, to report what he had seen and "to summon immediate help," Larkin wrote.

Telling his wife to stay inside, silent and away from windows, Kelly went onto his porch with his rifle.

"The leader of the armed group of men saw Mr. Kelly and pointed an AK-47 right at him," Larkin wrote. "Mr. Kelly, fearing for his life and safety, fired several shots from his rifle, hoping to scare them away from him, his wife, his animals, and his home. As he shot, Mr. Kelly took care to aim well over the heads of the armed group of men. The group then began running into the desert surrounding his home. Once the group had fled, Mr. Kelly walked over to his barn to see if it was safe and secure."

Border shooting court hearing

George Alan Kelly, 73, is charged with first-degree murder for allegedly shooting a Mexican national on his ranch just north of the border. (Santa Cruz County Clerk of the Court )

The filing notes Kelly had a second conversation with the Border Patrol ranch liaison that ended at approximately 2:36 p.m. Even though Kelly reported that he heard a single shot and that the men he had seen were armed, the liaison "incorrectly reported" that Kelly stated he could not tell whether the men were armed or not, Larkin wrote. The radio dispatch to the Border Patrol agents en route to the property at approximately 2:40 p.m. "correctly reported that armed men had been seen in the area."

While Kelly was checking his barn, a number of Border Patrol and Santa Cruz County Sheriff's deputies arrived at the property and encountered Kelly, who indicated to them that he had seen a group of armed men near his house, the filing says. Deputies also made contact with Kelly’s wife, who indicated that she had seen armed men carrying large backpacks near the house, Larkin wrote.

Border Patrol agents and sheriff's deputies walked "all over" Kelly’s property but found no one, the filing says. They also used various cameras to try to locate the men but were unsuccessful. Law enforcement then left.

Border patrol ride horses near Nogales

Defense says Kelly contacted the Border Patrol Ranch Liason when he spotted armed men in the trees near the home on his Arizona property.  (John Moore/Getty Images)

As the sun was going down later that day, Kelly went to his pastures to check on his horse, still concerned the horse might have been injured in the incident. Noticing that the dogs he took with him were focused on something on the ground near a mesquite tree, Kelly approached the area and "observed a body lying face down in the grass," Larkin wrote. He then called the Border Patrol ranch liaison a third time to report the discovery and request assistance from law enforcement.

When law enforcement arrived, Kelly helped them find the body and cooperated with their investigation, according to Larkin. The investigation found that the body was that of a male "foreign national" who did not have any firearms or backpack on his him. The cause of death appeared to be a single gunshot wound, and it appeared the body was fresh, according to the filing.

"The person [had] a radio with him, and he was wearing tactical boots, indicating he was possibly involved in illegal activity," Larkin wrote.

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The defense attorney added that it remains unknown what kind of bullet caused the fatal wound, what was the time of death, how long the body had been there or where and what position the person was in prior to receiving the fatal wounds. In an interview with law enforcement, Kelly "admitted to firing warning shots at the smugglers earlier in the day, but he denied firing any shot directly at any person," Larkin wrote. "He does not believe that any of his warning shots could have possibly hit the person or caused the death. All of the shooting that Mr. Kelly did on that date of the incident was in self-defense and justified."

Kelly and his wife have lived on their property outside Nogales, Arizona, for more than two decades.