The Brooklyn slumlord whose body was found smoldering in a Long Island dumpster owed more than a million dollars to loan sharks, in addition to the millions he owed in real-estate investments, a partner told investigators working on the case.

Israel “Sam” Perlmutter — a business associate of slain Menachem “Max” Stark — told detectives they owed money to characters who could be involved in the man’s abduction and brutal killing, according to law-enforcement sources.

The Post had earlier reported that the duo defaulted on a $29 million real-estate loan in 2008, an issue that was the subject of an ongoing court battle.

Stark was killed by “compression asphyxiation” when at least one assailant sat on him inside the light-colored Dodge minivan that was used to flee the scene outside his Williamsburg office, the sources said.

His partially burned body was found in a Great Neck, LI, gas-station garbage bin Friday. Sources said the widespread burns were inflicted “after the fact,” possibly when the killers set the trash ablaze to try to cover up the crime.

Stark ran rental properties riddled with code violations, racked up huge debts and sidelined as a loan shark, sources said

A surveillance camera recorded how he battled his kidnappers for about five minutes Thursday night before he was duct-taped and shoved into the van, but blinding snow obscured the license plates and the assailants’ faces.

Law-enforcement sources said Monday that cops had obtained telephone records for Stark’s cellphone, office and home, and were poring over the logs to identify potential suspects.

Also Monday, Stark’s family increased the reward for information about his murder to $25,000.

“We beg you, whoever knows anything or thinks they know anything — for your own sake, for the sake of your brothers and sisters, citizens of New York City, the human race — come forward,” Rabbi David Niederman of the United Jewish Organizations of Williamsburg said.

Meanwhile, Perlmutter, 42, apparently went into hiding after talking to investigators, fearing Stark’s killers may be coming for him next.

Law-enforcement sources said Monday that cops had obtained telephone records for Stark’s cellphone, office and home, and were poring over the logs to identify potential suspects.

Police sources said that Perlmutter has been cooperating with investigators and is not a suspect at this time.

Additional reporting by Amber Sutherland and Laurel Babcock