According to NBC News, the 'horrible, horrible accident' happened when the toddler found a loaded semi-automatic handgun under the sofa.

The bullet went through his mother's head, as she changed his baby sister's nappy.

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"The grandmother came in and supposedly found the two children covered in blood," a neighbour told a local television station.

The toddler, traumatised by the incident, apparently kept repeating just two words as police loaded him into a car.

"Mummy shot."

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Engles' husband, a truck driver who was on the road, arrived home yesterday evening after hearing about the shooting and was only able to confirm his wife's death by repeatedly calling the hospital.

Officer Dave Walker has said that police will treat the incident as a 'horrible' accident.

He said: "We are prepared to do what we have to do to keep the kid safe - we think this is a horrible, horrible accident."