DALLAS COUNTY, Texas  (CBSDFW.COM) – At the entrance to a make-shift mobile home park in far southern Dallas County, a weathered sign warns drivers to go ‘slow’, ‘kids at play.’

Just beyond it, police tape secured the crime scene where investigators believe 2-year-old old Anthony Isaiah Mares had been killed.

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“The whole thing is just a tragedy,” says Ellen Waterhouse, who also lives on Beckleycrest. “It’s just sad. Breaks my heart. I can’t imagine her pain.”

Orlando Hidalgo, 22, was arrested Monday and charged with capital murder in the death of his girlfriend’s son.

Orlando Hidalgo

Anthony was pronounced dead at Charlton Methodist Hospital Sunday night after family members rushed the child there.

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According to investigators with the Dallas County Sheriff’s Department, a tip led investigators to a home in the 9400 block of Newhall, where they recovered a murder weapon and shell casings.

The toddler’s family lived in the 9600 block of Beckleycrest and police investigators spent hours there Monday collecting evidence.

Meanwhile, Hidalgo’s relatives are defending him.

His mother told CBS 11 today that her son is innocent and claimed that the toddler found the gun and accidentally shot himself.

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The Sheriff’s Department says the investigation is ongoing.