A man who told two homicide detectives that he shot his father to death early Saturday at a house in north Fort Worth raised a defense of a third party rationale, saying that he believed the elder man was threatening to kill the shooter’s mother and grandfather, who were inside the house.

Johnathan Hernandez, who is 24, said that he was outside a garage when he heard his father, Nicacio Hernandez, speak while inside it.

“Y’all are all gonna die tonight.” Nicacio threatened, his son recalled during the interview with Fort Worth Police Department Detectives Domingo Martinez and Michael Sones five hours after the killing about 3:30 a.m., according to the affidavit that the detectives prepared to support a murder arrest warrant for Johnathan, whom other officers arrested on Saturday afternoon.

Johnathan said that he then aimed a rifle at the back of Nicacio’s head and fired multiple rounds at him through the garage window in the 8300 block of North Riverside Drive, according to the affidavit. Five ejected cartridge casings that a police crime scene officer documented collecting from the property suggest the diameter of the associated projectile is 7.62 millimeters.

Nicacio, who was 41, died on the ground in the doorway leading from the garage into the house.

Johnathan told the detectives that, through windows, he saw his father inside the garage, facing away from him and standing near the door.

The affidavit in the patricide does not offer an account of all of the evidence in the case. The document does not, for example, indicate whether the detectives believe that, as Johnathan alleged in the interview, Nicacio pulled a knife on his son and fired a gun at him on the morning of the homicide. The affidavit does not describe the detectives’ interviews with the shooter’s mother and grandfather in depth. Detective Martinez wrote that the conversations “did not reveal any facts indicating that Nicacio posed an immediate threat to either of them when Johnathan shot him.”

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The suspect interview account in the affidavit describes a flare of anger between the father and son in the hours before the killing.

On Friday night, Johnathan and his parents were at Tumbleweeds sports bar near NE Loop 820 and Blue Mound Road when Johnathan became involved in a disagreement with a friend of Nicacio. Johnathan said in the interview that Nicacio took the friend’s side, which angered Johnathan because Nicacio was his father, according to the affidavit. The disagreement was eventually resolved.

Johnathan, Nicacio, and Johnathan’s mother, whose name police redacted from the version of the affidavit it released to the press, returned to the North Riverside Drive house. There, Johnathan told Nicacio that he did not appreciate Nicacio taking his friend’s side during the earlier disagreement instead of supporting him as his son.

According to Johnathan, this angered Nicacio, who then approached him. Johnathan said that he believed Nicacio was about to hit him. Johnathan responded by punching Nicacio in the head about five times.

Johnathan said that after being hit, Nicacio removed a fixed-blade knife from a sheath on the elder man’s belt. Johnathan became afraid that Nicacio would injure him and left the house through the garage, according to the affidavit.

As he ran, Johnathan said, he heard a gunshot when he was about 100 yards from the house. He turned and saw Nicacio and Johnathan’s mother standing in the driveway. Johnathan believed Nicacio had fired a gun at him, he told police.

Johnathan told Detectives Martinez and Sones that he got a ride to his apartment, also in Fort Worth, picked up a rifle and drove himself back to his parents’ house, where he shot his father.