CHILLING new revelations about the crazed Connecticut school shooter ADAM LANZA have been un­covered during an exhaustive ENQUIRER investigation.

In a world exclusive interview, the man who built the home where killer Lanza lived has disclosed pri­vate details of the basement bunker where the 20-year-old plotted his bloody massacre at Sandy Hook Elementary School.

Contractor Robert J. Riebe recalls meet­ing young Adam when he sold the property in New­town, Conn., to the Lanza family. Little did he realize back then that the child would someday slaughter 26 people at a school, including 20 first-graders, before committing sui­cide in a criminal act that stunned America.

“I remember Adam,” Riebe told The ENQUIRER.

“It gives me chills when I think that I shook his hand. He was just a little kid back then.

“Nothing out of the ordinary or remarkable.

“I couldn’t believe it when I heard the news. I was shocked.”

Riebe built the four-bedroom, three-bath, two-story home on 2.19 acres at 36 Yogananda St., and sold it for $405,900 to Lanza’s parents, Nancy and Peter, in July 1998.

One thing that stuck out in Riebe’s mind was an odd remark that Nancy Lanza made.

“She told me straight up that she owned a hand­gun,” he recalled.

In the weeks since the mas­sacre, it’s been revealed that Adam Lanza often holed up in the basement of his home for hours, playing violent video games while surrounded by military post­ers.

The bunker-like room in­creasingly became “ground zero,” where his twisted mind plotted the massacre which began on the morn­ing of Dec. 14, when police say he pumped four bullets into his mother’s head while she slept upstairs.

“The basement could easily be a place where someone could spend long hours,” Riebe, 49, told The ENQUIRER.

“It was finished off with sheet­rock walls and painted off-white. The space was cozy, covering some 500 square feet. It also had a separate mechanical room for the furnace, and some extra space for storage. The washer and dryer were upstairs, so there was plenty of usable area.”

A local Realtor told The ENQUIRER that the house will probably wind up selling for just a fraction of its $600,000 value.

“It would be like living in a cemetery or entombed in a crypt, with a constant reminder that this place is associated with the school slaughter,” said the real estate agent.

“The karma is just too bad to overcome. I wouldn’t be sur­prised if whoever buys it tears it down and builds a new house on the land.”