SURFSIDE, Fla.—Search-and-rescue efforts stretched through a sixth day on Tuesday at the site of a collapsed Florida condominium complex where at least a dozen people died and 149 more remained missing amid fading hopes of finding anyone else alive. 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 give way abruptly early on Thursday as residents slept. Initial attention has focused on structural deficiencies described in a 2018 engineer’s report. In April 2021, the condominium association’s president warned residents that concrete damage identified in the report had “gotten significantly worse” and urged them to pay some $15 million in assessments needed to make repairs, according …