The Houston mother of a 9-year-old who was shot dead while inside the family pickup truck earlier this week expressed regret for not yelling "get down" louder during the shooting.

Arlene Alvarez, 9, was in the vehicle that got stuck by bullets after an armed robbery at an outdoor ATM, Fox 26 of Houston reported.

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"Duck down, Arlene,'" added Gwen, Arlene's mother, according to the report. "'Duck down, Arlene.' I didn't scream loud enough. I didn't know she had her headphones on."

The girl's father, Armando, said he also urged his three children to "get down," ABC 13 of Houston reported

Tony D. Earls, 41, is formally charged with aggravated assault - serious bodily injury, after fatally shooting Arlene Alvarez, 9.

Tony D. Earls, 41, is formally charged with aggravated assault - serious bodily injury, after fatally shooting Arlene Alvarez, 9. (Houston Police Department)

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Police said Tony D. Earls, 41, was robbed and fired at the vehicle he incorrectly thought the suspect entered. The girl was taken to a hospital and was declared brain-dead, before her family decided to remove her life support, Fox 26 reported.

Earls was arrested later and has been charged with aggravated assault serious bodily injury, police said. He was subsequently released from jail after he posted his $100,000 bail on Thursday night, officials added.

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The family is seeking justice against Earls, whose actions did not meet the standard for self-defense, according to the family’s attorney, Rick Ramos, ABC 13 reported.

"Once you take your gun and you run off and you have your back turned to the individual you robbed, that individual is no longer an immediate threat or fear of imminent safety," Ramos said, according to the report. "At that point in time, you lose your right to self-defense because the threat is gone."