Police and firefighters in Oakland, California, are using surveillance tools like drones, usually reserved for criminal investigations, to ascertain damage and identify victims from a deadly fire that broke out Friday night.

The blaze engulfed a local warehouse, dubbed "Ghost Ship," which had unofficially been converted to a music venue. The structure fire is believed to be among the worst in the country in recent years.

At a 3pm press conference on Sunday, Sgt. Ray Kelly of the Alameda County Sheriff’s Office said there had been 33 official deaths recorded, and he estimated that "35 to 40 percent" of the building had been searched and was still being searched.

"I want to assure you that we are continuing to operate a 24/7 operation to effectuate the removal [of victims' bodies]," Mayor Libby Schaaf said. "And we are supporting the families and loved ones."

She also added that the county district attorney had activated its criminal investigation team—the building was not permitted for parties and may have housed unauthorized residents.

On Sunday, according to local reporters, the county coroner asked families to preserve samples of their loved ones' DNA so that they can compare them against samples found in the rubble.

The Alameda County Sheriff’s Office, which did not immediately respond to Ars’ request for comment, was seen on Saturday morning deploying at least one drone to examine remaining “hotspots” on the warehouse on 31st Ave.

Drone from @ACSOSheriffs office checking for hotspots at #oaklandfire. 9 confirmed fatalities, as many as 25 unaccounted for. pic.twitter.com/5cfKsHvpzC — Christien Kafton (@CKaftonKTVU) December 3, 2016

As Ars has reported before, the ACSO has six drones that it often uses in conjunction with neighboring law enforcement and other first responder agencies.

The Oakland Police Department has also been taking down license plates of cars parked nearby the venue at the time of the blaze as another way to identify victims.

OPD did an area-wide search, gathered license plate numbers of parked cars trying to ID victims who drove to warehouse party #OaklandFire pic.twitter.com/t25vyfPwCH — Darwin BondGraham (@DarwinBondGraha) December 4, 2016

The OPD, which did not immediately respond to Ars’ request for comment, has an active license plate reader program—special devices mounted atop 33 police vehicles that can scan plates at very high speed. In August 2015, the agency reduced the time that it retains such information, from an unlimited period to six months.