Heavy machinery used in macabre dig at Rex Heuermann’s home

Investigators continued using heavy machinery to dig up the yard of suspected serial killer Rex Heuermann Monday — as police revealed his blasé first words when he realized that he was finally being arrested.

A backhoe was seen early Monday continuing the macabre dig at Heuermann’s Massapequa Park home — where The Post revealed a suspected soundproof room was found in the married dad of two’s basement.

Officers wearing white lab-style protective suits continued the painstaking search for possible buried evidence with the help of cadaver dogs and specialized sonar devices.

They are looking for “trace evidence, blood, DNA” as well as possible “trophies,” Suffolk County District Attorney Ray Tierney said last week.

“Normally, people keep mementos of significant times in their life, so that’s what we’re looking for,” the DA told Newsday on Thursday.

The heavy machinery brought in over the weekend marked a major intensification of the search that started 12 days ago when the architect was busted outside his Midtown Manhattan office.

Officials have yet to reveal if the ongoing dig and intense search of Heuermann’s home — as well as his office, vehicles and other properties, in South Carolina and Las Vegas — has unearthed new alleged evidence likely to be key in the case.

Suffolk County Police Commissioner Rodney Harrison refused to discuss it with NBC News in an interview that aired Monday, only noting the “disturbing” discovery of more than 200 guns.

However, he revealed how dismissive Heuermann, 59, had been when he was busted murdering three of the “Gilgo Four,” and named the prime suspect in the fourth.

“He very much said, ‘What am I here for? I don’t know nothing of what you’re talking about,’” the top cop said.

Harrison previously said that part of the reason Heuermann was busted in Midtown was “to see if we could catch him by his workplace, take that long ride from 35th and Fifth out to 30 Yaphank — which could be a one-and-a-half-hour ride — and see if he could talk and give up anything.”

Instead, “He asked for a lawyer — and that was the end of the conversation,” Harrison said, telling People that the suspected killer “kept to himself” and made “no statements” when taken into custody.

Once booked into jail, he reportedly only asked, “Is it in the news?”

Heuermann’s wife of 25 years, Asa Ellerup, also 59, filed for divorce days after his arrest. She’d been “disgusted,” “shocked” and “embarrassed” at the news — before telling officers, “OK, it is what it is,” Harrison previously said.

Heuermann has pleaded not guilty to three counts of murder in the deaths of Amber Lynn Costello, 27, Melissa Barthelemy, 24, and Megan Waterman, 22. He has been named “prime suspect” in the death of Maureen Brainard-Barnes, 25, and police continue to examine other cold cases.