Police Chief William McManus told a news conference Monday that authorities received a call at about 5:50 p.m. local time from an employee who had heard cries for help and found the trailer with its doors partially open. The worker found a series of corpses inside the trailer, McManus said. McManus said three people were in custody, although he noted that authorities were not sure they were involved. The incident is now under federal investigation. San Antonio Fire Chief Charles Hood said the 16 people taken to the hospital were all conscious when they were found, although they were “weak” and could not leave the trailer on their own. He said everything was “hot to the touch” and he suffered from heat-related injuries such as heat exhaustion and heatstroke. He said there were no signs of water or air conditioning in the truck and authorities said it was unclear how long the team had been in the truck before they were found. The victims were a combination of men and women and differed in age, but none of the dead appeared to be minors, officials said. On Tuesday morning, Mexican Foreign Minister Marcelo Ebrad said on Twitter, citing US authorities, that the victims included 22 Mexicans, 7 Guatemalans and two Hondurans. The other victims had not yet been identified, Ebrad said. Hood said the first responders were informed to help them process what they saw. “You should not open a truck and see stacks of corpses in there,” he said. “None of us come to work imagining something like this.” San Antonio Mayor Ron Nuremberg called the situation “a horrible human tragedy.” Immigrants seeking asylum must always be treated as a humanitarian crisis, but tonight we are facing a horrific human tragedy. More than 40 promising lives were lost. I urge you to think with compassion, to pray for the dead, the sick and their families right now. – Mayor Ron Nirenberg (@Ron_Nirenberg) June 28, 2022 Homeland Security is investigating the alleged human trafficking incident and will work with the San Antonio Police Department, law enforcement officials told CBS News. DHS said in a statement that “it is a horror for this tragic loss of life near San Antonio. It speaks to the desperation of immigrants who would give their lives at the hands of intolerant traffickers who do not respect human life.” An ICE spokesman said in a statement that Internal Security Investigations responded to the scene following a call from the police department. The spokesman said more details would be made public as the investigation continued. More than 20 emergency vehicles responded to the scene, the CBS subsidiary KENS-TV said. More