He’s one twisted monster.

Dimitrios Pagourtzis war-whooped “Woo-hoo,” blared a WWII Japanese military anthem on his phone and shouted cruel taunts as he opened fire on his cowering classmates, according to new accounts a day after the Texas high school junior allegedly killed eight students and two teachers.

The admitted gunman even chillingly sang “Another one bites the dust!” as he fired away with his father’s Remington 870 shotgun and .38-caliber handgun.

“My friend Trent was in the classroom and said after [Pagourtzis] would shoot a student he would sing, ‘Another one bites the dust!’” Sante Fe High School sophomore Kole Dixon, 16, told The Post of a classmate, whose last name he asked not be printed.

“He also kept playing a kamikaze song over and over as loud as he could,” on his cellphone, Dixon said of the shooter.

Pagourtzis had the same kamikaze military anthem on his now-deleted YouTube page, Dixon said.

Pagourtzis had earlier bragged of wearing a “Rising Sun” insignia on his black trench coat, explaining it signified “Kamikaze Tactics,” according to a photo and text posted on his also-deleted Facebook page.

New details of the 17-year-old’s sick sense of humor went well beyond the previously reported “Born to Kill” T-shirt he wore, and his taunt of “Surprise!” as he blasted through the walls of an art class supply closet.

“They hear the gunman in the classroom next door yelling Woo Hoo! and firing more shots,” mom Deedra Van Ness said in a Facebook post Friday night, recounting details from her by her daughter Isabelle, who survived unscathed but was covered in blood.

“Surprise, motherf–ker!” the shooter hollered as he fired into the closet wall, instantly killing two of the half-dozen students who had barricaded themselves inside with Isabelle, Van Ness said her daughter told her.

“Are you dead?” he later asked from the other side of the closet.

“Do you think it’s for you?” he also joked, as cell phones left behind in the classroom rang unanswered.

County officials revealed that Pagourtzis exchanged “a lot of firepower” with authorities before surrendering. Despite this alleged show of firepower, Pagourtzis purposefully collapsed while giving himself up — so he wouldn’t be shot by his arresting officers. The shooter, “sort of fell to the ground and surrendered,” said Republican Texas Rep. Michael McCaul.

So-called “explosive devices” found in the school and in Pagourtzis’ car and home were duds — incapable of detonating, Texas officials said. The devices included carbon dioxide canisters tapped together, and a pressure cooker with an alarm clock and nails inside.

Two of the 13 people injured in the shooting remained in critical condition. They include one of the three school security officers who engaged Pagourtzis prior to his surrender.

The officer, retired Houston police officer John Barnes, had been shot in both arms. He was pulled to safety by a second school safety officer, who then applied a tourniquet. Barnes had suffered extensive bleeding. Doctors have since told his family that his injuries are probably not fatal, his former colleague, Houston Police Capt. Jim Dale, told reporters.

The suspect’s ex-girlfriend may also have been among those shot, sophomore Kole Dixon told the New York Times. But Dixon told The Post he didn’t know the girl’s name, and had heard about her shooting second hand.

Pagourtzis, who police say admitted to the 30-minute shooting and is cooperating with authorities, remains held without bail on capital murder charges. Officials are still not clear whether Pagourtzis acted alone. Harris County Sheriff Ed Gonzalez said officials have questioned another student, whom he described as a person of interest. Two other individuals may have useful information, he said, without giving details.

A middle school honor roller and former junior varsity football defensive tackle, Pagourtzis in recent weeks had taken to bragging of owning knives and wearing a black trench coat — decorated with a German Iron Cross pin and other military insignia — even in sweltering weather.

Still, he had given no outward signs of planning an attack, officials said Saturday.

After the attack, he appeared “weirdly non-emotional,” his lawyer, Nicholas Poehl told Reuters.

“There are aspects he understands and there are aspects he doesn’t understand,” said the lawyer.

Pagourtzis’s parents issued a statement saying they are “as shocked and confused as anyone by these events that occurred.”

They called their son a “smart, quiet, sweet boy.”

Said their lawyer: “I think every parent probably instinctively knows they don’t know everything about their kids, but when you find out something like this … it’s extremely hard.”

“These people are victims too. They didn’t know, they didn’t expect and they surely didn’t predict it. So, prayers to everyone in this whole mess.”

Students were briefly allowed back inside their bullet-pocked school, located about 30 miles southeast of Houston. The students were taken inside in groups of no more than 10, escorted by local police officers, so that they could retrieve car keys, phones and other belongings.

Additional reporting by Brad Hamilton with Post wires