Featurepics.com File photo: The Bullmastiff isn't bred to attack, unlike the pit bull terrier, but it is considered an assertive guardian dog that shouldn't be left alone with children.

A 5-year-old boy was killed when a 150-pound dog attacked him in Arkansas, where he was staying with family friends after his family's home was destroyed by a tornado that devastated Moore, Okla., last month, authorities said.

The boy, whose name hasn't been released, was pronounced dead at a hospital Sunday after the dog attacked him about noon (1 p.m. ET) at a home in Jessieville, about 50 miles west of Little Rock, Garland County sheriff's deputies said.

The dog ran off, and county animal control officers searched for it Sunday and Monday. The dog's body was found Monday afternoon after a friend of its owner shot it dead, authorities said.

The boy and his 2-year-old sister were staying in Jessieville while their parents worked to rebuild after a powerful tornado killed 24 people and injured almost 400 others May 20 in Moore, near Oklahoma City.

"To me, it's heartbreaking," Garland County sheriff's Deputy Scott Hinojosa told NBC station KARK-TV of Little Rock. "I've got a 5-year-old daughter. You can't imagine what this family and friends are going through right now."

Authorities said the boy was upset and crying, which the dog, a Bullmastiff, possibly interpreted as an aggressive act.

The dog's owner, Lynn Geiling, 50, a friend of the children's parents, told investigators she tried to pull the dog off the boy but got there too late. He was pronounced dead at Mercy Hospital in Hot Springs with severe lacerations to his head and his neck.

Hinojosa said Monday that no decision had been reached on whether Geiling and her husband would face charges.

The Bullmastiff isn't the same breed as the notorious pit bull terrier, which has often been bred to be an aggressive fighting dog. But it is bred to serve as a watchdog and to protect the home. The American Bullmastiff Association says the breed needs no special training to "react appropriately if his family is threatened."

"Never leave a child unattended with your Bullmastiff," the association warns on its website. "They are pack animals and will find their natural place in the pack if left to natural processes. That place may be at the top of the pecking order instead of below younger family members if left unchecked."

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