San Antonio - San Antonio-based US Attorney Richard Durbin jnr says those responsible for the deaths of eight people inside a sweltering tractor-trailer truck outside a Walmart store are "ruthless human smugglers indifferent to the well-being of their fragile cargo".Durbin says those inside the truck were helpless in the punishing almost 38°C heat and were victims of a "smuggling venture gone horribly wrong".He says federal investigators will work with San Antonio police to identify those responsible.After daybreak on Sunday, the truck remained at the side and toward the back of the store. The scene is marked off with yellow crime-scene tape and with officers and patrol cars. San Antonio Fire Chief Charles Hood says the many injured survivors taken from the tractor-trailer were suffering in varying degrees from such injuries as heat stroke and dehydration.Hood told journalists at the scene that paramedics and firefighters who treated the victims found all had accelerated heartbeats when they were taken from the truck in the stifling heat. "They were very hot to the touch. So these people were in this trailer without any signs of any type of water," Hood says.In video authorities posted online, Hood stood against a backdrop of flashing emergency vehicle lights in the pre-dawn hours as he briefed reporters. He says police and fire officials treated it as a "mass casualty situation" much like an plane disaster.In addition to the eight dead, Hood says, there were at least 30 others aboard the truck. Of those survivors, at least 20 people were in extremely critical or serious condition and the others had lesser injuries.