The Watch Stopped at 11:12: Data Recovered From a Tahoe Avalanche Victim’s Wristwatch Offers New Insight Into His Final Moments… 👇👇

The avalanche that killed at least eight skiers near Lake Tahoe is now under investigation for possible criminal negligence, as it becomes the deadliest in the U.S. since 1981.

In a statement, the Nevada County Sheriff’s Office said it has launched a parallel investigation into whether criminal negligence was involved in the Tuesday, Feb. 17 avalanche near Castle Peak, CBS News reported.

The probe is separate from the coroner’s death investigations, and officials cautioned it is too early to determine whether any charges will be filed.

The avalanche struck around 11:30 a.m. Tuesday in the Castle Peak area of Tahoe National Forest, about 10 miles north of Lake Tahoe, as a group of 11 clients and four guides was concluding a three-day backcountry ski trip, PEOPLE previously reported.

The group was traveling during a powerful storm that dumped up to 7 feet of snow and brought winds of up to 60 mph to the Sierra Nevada mountains, according to CBS.

Sheriff Shannan Moon said, per the outlet, that authorities are working to determine why the group continued its trip after an avalanche watch was issued Sunday and an avalanche warning was issued early Tuesday alerting of “HIGH avalanche danger” and the potential for “large” avalanches in the backcountry.

Captain Russell Greene added that the avalanche “overtook them rather quickly,” CBS reported.

According to the outlet, nine members of the group were initially reported missing. Eight have been found dead, and one person remains missing but is presumed dead as of Friday, Feb. 20, per authorities. Six people survived, including one guide and five clients. Two survivors were hospitalized with non-life-threatening injuries.

Undersheriff Sam Brown told CBS that survivors went into “frantic mode” and were able to unbury three individuals who did not survive before rescue crews arrived.

Rescuers also received information through the iPhone SOS feature before reaching the group, PEOPLE previously reported.

Authorities have described the rescue operation as complex, with crews needing to position standby search-and-rescue teams in case a secondary avalanche is triggered. The area is remote, rugged backcountry with no ski patrol or marked trails, officials previously said.

California’s Division of Occupational Safety and Health is also investigating Blackbird Mountain Guides, which led the trip, CBS reported. The agency typically has up to six months to determine whether workplace safety citations will be issued.

Want to keep up with the latest crime coverage? Sign up for PEOPLE’s free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

Families of six of the victims, described as a close-knit group of mothers and wives on a professionally guided trip, said they have “many unanswered questions” following the tragedy.

The families said the women were experienced backcountry skiers who were fully equipped with avalanche safety gear and trusted their professional guides, per previous PEOPLE reporting.

The sheriff’s office has not announced any charges and no additional press conferences have been scheduled as of Friday.