A pit bull mix who passed behavioral tests attacked the daughter of his new Patchogue owner the day he was brought home and was euthanized hours later, authorities said Monday.

Animal lover Stephen Neira, 40, had found Alex Thursday on a website to rescue "death row" dogs and had 22 minutes to save the brown and white pit bull mix before he was to be euthanized at the Animal Care Centers of New York City.

It was Neira's first time taking in a pit bull, and he felt like a proud father when he decided to foster the dog and welcomed the 42-pound addition home on Sunday.

VideoDog adopted by LI family attacks daughter

But moments later, Alex sank his teeth into Neira's teenage daughter Briana's face and throat. She used her arm to protect her throat, and Alex bit her elbow also.

Briana, 16, remained Monday at Stony Brook University Hospital, where she underwent plastic surgery on her mauled lip, her father said.

"It was supposed to be a beautiful, beautiful day; instead my wife can't stop crying," Neira said. "We were giving the dog a new life."

advertisement | advertise on newsday

Alex was tranquilized by Suffolk police and taken by the Brookhaven animal shelter. With the agreement of Neira and one of two agencies involved in the case, the 2-year-old dog was euthanized Sunday, a town spokesman said.

The dog's remains are to be tested for rabies, a Suffolk County health spokeswoman said.

Shelter documents show the city shelter system had transferred ownership of the pit bull mix on Thursday to a Vermont group, Carolyn All Breed Rescue, which had highlighted Alex's plight on the rescue website Urgent Pets on Death Row.

"Our thoughts go out to the family," a city shelter spokeswoman said in a brief statement. "In the meantime, we are investigating this case for further details." Officials at the rescue group could not be reached Monday.

Neira, his wife and their three children had picked up the dog earlier on Sunday at the city's Harlem shelter.

Alex had been brought to the city shelter Aug. 30, and agency documents have conflicting information on his background, saying both that he was a stray and that he was muzzled when surrendered by his owner. Within four days, he was on the website for Urgent Pets on Death Row.

On the shelter's behavioral tests, Alex was deemed "sociable" and passed touch, food aggression and toy possessiveness tests, although he pulled on the leash and appeared frustrated at being confined in the shelter. "The behavior department feels that he can go to an average home," the shelter said.

Once the family brought Alex home Sunday, the father took their new family member for a walk. Then, Neira said, he let the dog run laps in the backyard to tire him out, then opened the door to the kitchen.

"He ran inside, slid across the floor, turned around, saw my daughter and jumped for her throat," the father said.

Neira said he grabbed the pit bull from behind and placed it in a choke hold.

advertisement | advertise on newsday

"I had to get it off my daughter," he said. "I had to end it."

Hearing Briana's loud screams, next-door-neighbor Bill Samulik, 42, said he rushed over to find Neira battling the dog in the backyard.

Thinking the dog was unconscious from his grip, Neira said, he flung Alex a few feet away but the dog attacked once more. Samulik said he held the back gate open for Neira, who fled from the charging dog.Just before Alex was tranquilized, he was rolling in the grass and coming when called as if the attack hadn't happened, Neira said.