STROUDSBURG, Pennsylvania (NY TIMES) - Four men charged with murder in the hazing death of a Baruch College freshman pleaded guilty Monday to being involved in a fraternity initiation ritual in which the authorities said the 18-year-old student fell unconscious and the other fraternity members delayed seeking medical aid.

The students had travelled in the winter of 2013 to the Poconos from New York City for a weekend retreat where potential members went through a physically brutal process to join Pi Delta Psi, an Asian-American fraternity.

The student who died, Chun Hsien Deng, was one of the pledges, and the authorities said he was knocked out after he was blindfolded, forced to wear a backpack weighted with sand and pummelled by other fraternity members as he tried to cross a frozen yard as part of the hazing ritual.

Almost two years later, Monroe County prosecutors announced that 37 people had been charged in connection with his death, many facing counts such as assault and hindering apprehension. Five of them, as well as the national fraternity itself, were charged with third-degree murder, which does not involve premeditation or a specific intent to kill. The charges against one of the five were reduced.

Four of the men who had been charged with murder- Kenny Kwan, 28; Charles Lai, 26; Raymond Lam, 23; and Sheldon Wong, 24 - appeared in court here Monday, where they pleaded guilty to reduced charges of voluntary manslaughter and hindering apprehension after reaching an agreement with prosecutors.

Kwan, Lai and Lam tackled Deng during the hazing ritual, and Wong was not physically involved, but had been responsible for organizing and overseeing it, prosecutors said.

Prosecutors declined to discussed the terms of their agreement. The men, who avoided talking to reporters as they left court, are scheduled to be sentenced on Dec 4.

Prosecutors reduced the charges for Daniel Li, who had also been charged with murder; his case has not been resolved. Li had cooperated with prosecutors. The national fraternity is still awaiting a trial on murder and other charges.

The case has been cited as an example of a growing insistence by prosecutors across the country to take a harder line in pursuing criminal charges after college students are killed while being hazed.

This month, 18 students at Penn State University were charged, including several facing counts of involuntary manslaughter, in the February death of a 19-year-old sophomore, Timothy Piazza, after a "pledge night" of drunken partying. Prosecutors said Piazza stumbled around drunk, falling headfirst down a flight of stairs; he was unconscious and visibly injured, but fraternity members stalled for hours before seeking help.

In Deng's case, he travelled about 100 miles with a group of pledges and full-fledged members to Tunkhannock Township, Pennsylvania, to spend the weekend in a large rental house, its brick-and-siding facade reminiscent of a traditional fraternity house - something Pi Delta Psi would never have at Baruch, a commuter school in Manhattan where Greek social organisations have a tiny presence.

On that frigid December morning, Deng, who was known as Michael, strapped on the backpack and put on the blindfold, following three other pledges in going through the gantlet, which was known as the "glass ceiling" and was said to represent the plight of Asian-Americans. Unlike the others, though, Deng had been defiant, riling the fraternity members by kicking one of the men lined up to tackle him and not saying things he was supposed to, according to a grand jury report released in 2015.

The fraternity members reacted aggressively, pushing him to the ground, investigators found. One of them ran into Deng from 15 feet away, with his head lowered in a move known as the spear.

He was knocked out and the others in the group carried him into the house, his body stiff and feeling like "dead weight," according to the report. They laid him by a fireplace, changed his clothes and tried to get him to drink water and eat chocolate in an attempt to revive him. His breathing became laboured.

Instead of calling for medical help, the report said, they called a national fraternity official, who instructed them to hide anything with the fraternity's symbol on it. One of the fraternity members later told investigators they had resisted calling for an ambulance because one of them had looked up the cost and they thought it was expensive, according to the report. They sought guidance by searching on the internet, using phrases like "concussion can't wake up".

An hour passed before three members drove Deng to a hospital themselves. Doctors found that he had suffered severe head trauma and that his body was covered in bruises; in court, prosecutors presented a photograph that showed Deng with his back discoloured.

Deng was placed on life support and died the next day.

The national fraternity has argued that the hazing activity was not sanctioned and was a clear violation of its rules.

Li, who had been president of the Baruch colony of Pi Delta Psi and was one of the men charged with murder, testified at a hearing in 2015 that he and other fraternity leaders knew the ritual was against the rules, but that it was deeply ingrained in the fraternity's culture.

"In reality, they knew what was going on," Li said of the national leaders of Pi Delta Psi.

Officials at Baruch responded to Deng's death by permanently barring Pi Delta Psi and instituting a moratorium on pledging for every Greek social organisation on campus until next year.