All nine people killed in February’s catastrophic avalanche near Lake Tahoe suffocated after being buried beneath five to six feet of snow, authorities confirmed this week.

The revelation came as the Nevada County Sheriff’s Office closed its investigation into possible criminal negligence surrounding the disaster and sent its findings to the county prosecutor for review.

The Feb. 17 avalanche struck a 15-member backcountry group near Castle Peak during a historically intense blizzard.

The group included six clients and three guides with Blackbird Mountain Guides, while five others in the party, including one guide and four clients, survived.

On the day of the disaster, snow forecasters had issued a dire warning telling people to stay out of the backcountry because of the extreme avalanche danger.

Despite those warnings, the Blackbird group traveled too close to Perry’s Peak, a slope loaded with rapidly falling snow.

A roughly 100-foot-wide wall of snow broke loose and raced about 400 feet down the mountain, burying all but two members of the group.

The survivors scrambled to dig through the debris.

They managed to rescue four companions before deciding they could no longer reach the others.

As the blizzard worsened, they turned their attention to keeping themselves and two injured skiers alive.

An incident report published by the Sierra Avalanche Center, which had issued the avalanche warning, found that the group violated avalanche protocols during its attempt to leave the backcountry.

The first search-and-rescue crews reached the scene around 5:36 p.m., after authorities received word of the avalanche at about 11:30 a.m.

Rescuers dug out eight of the nine victims that day.

But with heavy snow hammering the area, they eventually placed the bodies together beneath a tarp, recorded their location with GPS coordinates and marked the spot with long poles used to search for avalanche victims.

The crews finished around 10 p.m.

The blizzard then prevented further recovery efforts for two days.

On Feb. 20, teams returned to the avalanche site, recovered the eight bodies and located the ninth victim.

All nine were airlifted to Frog Lake Huts, the backcountry lodging where the group had stayed for two nights before the avalanche.

The bodies were then transported out by snowcat and taken to a mortuary in Truckee.

Partially redacted coroner’s reports released Thursday list asphyxiation caused by snow burial as the cause of death for all nine victims.

Sections describing the condition of the bodies were redacted.

The sheriff’s findings now sit with prosecutors.

A prosecutorial review is the normal next step in a criminal investigation and does not necessarily mean charges will be filed.