Two brothers were fatally gunned down in their Mastic Beach home Friday afternoon, leaving detectives an “extensive” crime scene and no obvious suspect.

Blake Chambers, 28, was found with a gunshot wound when officers responded to his Huntington Drive home after a 911 caller reported two were shot about 12:25 p.m., police said.

His injured brother, Codi Chambers, 22, appeared to be in better shape and was being driven to the hospital by two people, including a resident of the house, when they saw ambulances arriving and doubled back to the house, police said.

“I just heard the one loud bang,” recounted a man, who declined to give his name but said he lives around the corner. “The police were on it like that.”

The brothers were pronounced dead at Brookhaven Memorial Hospital Medical Center in East Patchogue.

Homicide detectives worked late into the night to gather evidence at the house, where the brothers lived with their mother and others, police said.

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“We don’t know what the motive was right now,” said homicide Det. Lt. Kevin Beyrer.

“We’re still processing the scene and trying to determine where it happened. It’s an extensive scene.”

No weapon has been found and investigators don’t know how the shooter got inside, Beyrer said, and as of Friday night detectives had barely begun digging into the brothers’ history.

“We’re looking into backgrounds,” he said. “We’re looking into who might have wanted to do this. We’re investigating all aspects of these victims’ lives.”

Beyrer said no suspect had emerged from the early investigation and he declined to say about how many shots were fired and where the brothers were gunned down in the house.

The victims’ family could not be reached.

The house has long been the talk of the block and had the reputation as a place where cocaine, marijuana and oxycondone were sold, residents on the street said. Sometimes the smell of marijuana was in the air, neighbors said, more than once, someone shot up the Chambers’ family cars.

Neighbor Ted Holmes said he saw one of the car shootings years ago and would often notice “high class” vehicles making “discreet” deliveries to the house every two weeks or so.

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But the Chambers family never bothered their neighbors and were friendly, he said.

“That’s why people weren’t calling the police all the time,” Holmes said.

Both men had criminal records, according to court records.

Blake Chambers, who has had two orders of protection filed against him, has pleaded guilty to misdemeanors, including criminal possession of a weapon and assault, and was sentenced to 8 months in jail for a felony, attempted criminal sale of a controlled substance, court records show.

Holmes said Blake Chambers had turned his back on drugs and was trying to get a commercial license to drive a bus.

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Codi Chambers pleaded guilty in October to two felonies, including attempted assault with a weapon and intention to cause injury and criminal possession of methadone, and misdemeanor resisting arrest, according to online court records.

Anthony Rutkowski, who had initially represented the younger Chambers on the felonies, said he last spoke to his client a month or two ago and learned the man was going to be a father.

“He was expecting to start a family,” said the Southampton-based attorney. “He was soft-spoken and intelligent. Nobody deserves to die this way.”

Detectives ask anyone with information to call Crime Stoppers at 1-800-220-TIPS.