The death toll in the Maimi building collapse has risen to 12 with 149 people still unaccounted for as search-and-rescue efforts stretched through a sixth day on Tuesday at the site of the Florida condominium complex.

Remains of the 12th casualty in the disaster, which could rank as the deadliest accidental structural failure in U.S. history, were recovered on Tuesday, Miami-Dade County Mayor Daniella Levine Cava said at an afternoon news conference.

Investigators have not yet determined what caused a major section of the 40-year-old Champlain Towers South condo to collapse last Thursday as residents slept.

Florida emergency management director Kevin Guthrie said local authorities have asked the federal government to send additional urban search-and-rescue teams to the scene in the oceanfront town of Surfside, adjacent to Miami Beach.

Authorities believe survivors might yet be located in the pile of pulverized concrete and twisted metal left when nearly half of the 12-story, 136-unit tower caved in on itself.

“The rescue effort continues unabated except for that brief lightning storm we had today,” Surfside Mayor Charles Burkett said.

According to local10news, one of the first lawsuits to be filed against the ChamplainTowersSouth Condominium Association in response to the collapse was filed last week late Thursday following the collapse.

The lawsuit was filed on behalf of Manuel Drezner and “on behalf of all others similarly situated.”

The lawsuit, which was filed by the Brad Sohn Law Firm, alleges that the building’s association failed to “secure and safeguard the lives and property” of those who live at the building. They are asking that the victims are compensated after the collapse.

The news outlet also reports that another lawsuit was filed over the weekend. It was filed on behalf of Steve Rosenthal, who lived in Unit 705.

In his lawsuit, it says the association knew or should have known “the entire structure was deteriorating and becoming susceptible to catastrophic loss by collapse.” He is seeking more than $5 million in damages.