Darius Marshall had just finished a shift as a security guard at the United Nations when he called his banker brother, Eros, at his Tribeca office. But Eros was busy.

Darius “got off early and stopped by; I was on a project and couldn’t get away. I told him that I’d have to catch him next time,” he told The Post.

So Darius boarded the Andrew J. Barberi ferryboat at Whitehall Terminal in Lower Manhattan, and set off for his new home on Staten Island, where he had just moved with his wife of four months, Cindy.

Just two years earlier, Darius had barely survived the collapse of the World Trade Center on 9/11. He was knocked unconscious by falling debris and was finally found by his family on a hospital ferryboat in New Jersey 13 hours after the attacks.

This time, Darius would not make it.

Twenty minutes after leaving the tip of Manhattan, as the 3,335-ton, 310-foot-long Barberi approached the St. George Terminal, the off-course vessel plowed into a maintenance pier at full speed, piercing a 250-foot wide hole in its starboard side and ripping through the main deck where many of the 1,500 passengers, Darius included, lined up to disembark.

At 25, Darius Marshall was the youngest of 11 people to lose their lives that day. “He was my younger brother and my best friend,” said Eros Marshall said of the Wagner College graduate.

Oct. 15 will mark the 20th anniversary of the ferry tragedy, caused when the man at the ship’s wheel, Assistant Capt. Richard Smith, 55, blacked out at the helm after taking strong prescription medication for a bad back.

Seventy people were injured, some horrifically maimed.

Doctors at Staten Island hospitals performed amputations on four people, and treated untold broken bones, crushed pelvises and life-changing trauma.

James McMillan Jr., 44, of the Bronx, lost the use of his arms and his legs. Paul Esposito, 24, lost both legs above the knee.

In 2004, Esposito told The Post he still had nightmares but wanted to live a full life: “I want to have a positive attitude. I want to bring some good out of a bad situation.”

Barbara A. Butcher, an investigator with the city Office of the Chief Medical Examiner, was assigned to the case.

In 2004, Esposito told The Post he still had nightmares but wanted to live a full life: “I want to have a positive attitude. I want to bring some good out of a bad situation.”

“My first view of the destruction of the ferry was heartbreaking,” she recalled. “So many personal items strewn through the wreckage of the interior, and then the sight of human remains crushed beneath the seats and windows.”

Worse was to follow. “I remember telling a young wife that her husband was identified among the victims,” she recalls. “Her screams still echo in my mind.”

Eros Marshall returned to his home that night in Sparta, NJ, and turned on his television — his first glimpse of what had happened.

He called Darius, but only got his voicemail.

“I knew something was wrong,” he said. “My wife and I drove to a facility that the Red Cross set up on Staten Island. It took an hour or so before they told us that he had passed away in the accident.

“I wasn’t angry, I was devastated. I remember thinking – how am I going to tell my mother?”

In the immediate aftermath of the crash, Capt. Smith fled the scene to his home in Staten Island.