When Det. Anthony LaFemina got a call about a dog that died of serious injuries in Brooklyn late last month, his compassion immediately kicked into gear. But the case turned out to be even more disturbing than he had expected.

LaFemina, 28, was himself a dog lover who had rescued several pit bulls over the years.

So when he started to investigate, he knew something wasn’t right.

Prospect Heights resident Robert Haro first brought the 2- or 3-year-old dog, a female pit bull, to a local animal hospital on Feb. 24, claiming she got her head stuck in a fence and speculating that a raccoon might have bitten her. But the vet was suspicious, police said, and after being forced to euthanize the dog, called the cops.

“They forwarded me some pictures of the dog, and once I saw the pictures, that’s when I realized this wasn’t by accident,” LaFemina said.

The dog had what looked like deep bite wounds on her shoulder and neck, her ears had been chewed off and her back legs had holes in them. “It was a tough one.”

So LaFemina went to see Haro, who invited him in. That’s when the six-year NYPD veteran noticed a second pit bull chained up to a pole with injuries to her face — signs of dog fighting.

He presented the case to the Brooklyn district attorney’s office and got a search warrant to search the entire Prospect Place home.

On March 6, LaFemina, along with members of the Emergency Services Unit, found a house of horrors, police said.

In a backroom of the basement, they found Emma, the dog that was previously chained to the pole. But that wasn’t all: police uncovered a cache of weapons, including a rifle, handguns, high-capacity magazines, a crossbow and a dozen knives.

Haro was arrested and charged with animal cruelty and two counts each of criminal possession of a weapon and criminal possession of a firearm. He was held in lieu of $25,000 bail.

Attorney information for Haro was not immediately available.

LaFemina was able to rescue Emma, who is about 4 or 5 years old, and brought her to the ASPCA.

“She’s doing all right now, she’s just a little scared,” he said.

The officer is a stalwart defender of pit bulls.

“To me, everybody gives these dogs a bad rap and they’re probably the most loyal dogs that I’ve ever dealt with,” he said.

He added he had to pick up this case. “It was something that hit me, so I said, ‘You know what, I’m going to work it.’”