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HESPERIA, Calif. — A 4-year-old boy had his lower leg amputated after being attacked by his father’s police dog, according to a neighbor who helped save the child from the attack at a Hesperia home, KTLA reported.

The incident occurred Sunday at a home where Rialto Police Department Officer Michael Mastaler lives with his family and his K-9 partner, a lieutenant with the department confirmed.

Mastaler had returned home from a weekend training session with the dog, a Belgian Malinois named Jango, when he put the animal in the backyard and went upstairs to change clothes, believing his son was safely inside playing video games, police said.

Minutes later, neighbors heard the child screaming.

Neighbor Jeff Houlemard’s son saw the boy being tossed around by the dog, which had him by the leg.

Houlemard knocked down a tall wooden fence with his shoulder to get to the child, kicking Jango and then leaping on top of the K-9 when the dog did not release the boy, he said.

“I … just ripped his mouth open,” Houlemard said. “I just started choking the dog.”

Mastaler came running, and he and Houlemard attended to the boy’s mangled leg while Houlemard’s wife calmed the boy, practicing ABC’s and 123’s with him.

The boy was focused on his lip, which had also been hurt, Shannon Houlemard said.

The child was airlifted to Loma Linda University Medical Center, where a spokeswoman confirmed he remained on Thursday.

Eight inches of Mastelar’s son’s left leg were amputated.

“It is a serious and very tragic accident,” Rialto police Capt. Randy DeAnda told the Daily Press of Victorville. “Police K-9s are highly trained and usually work under the direct supervision of a handler. Here, there was obviously a timeframe where the dog was not supervised. It was not intentional; it was not an aggressive dog just wandering around.”

Jango was set to be quarantined for 10 days amid an investigation that will determine whether the dog should be euthanized, according to Rachel Molina, a spokeswoman for Hesperia Animal Control.

A “beware of dog” sign still hung from the fence surrounding the Mastaler family home’s backyard on Thursday.

Houlemard was a hero, his wife said, but that label was rejected by Houlemard who credits others who responded as well.

“Having kids of my own, hearing the screams that I heard, I just knew that I had to get to him,” Jeff Houlemard said.

A GoFundMe page set up Thursday morning to supplement the boy’s recovery had brought in more than $4,000 by early evening.

“The Mastaler family appreciates the overwhelming love and support,” the page stated.

Mastaler became a K-9 handler in the January 2014, according to the Rialto Police Department website.

Jango was born and trained in Holland, and his commands are in Dutch, the website states.