Two men who suffered burns in a Wednesday night fire that killed two young women are now in police custody, suspected of running a meth lab. Investigators told 7NEWS Thursday morning that they have collected enough evidence to conclude that the victims were running a meth lab in the basement of a duplex located on Alameda and Lincoln. Sgt. John Pender of the Denver police narcotics division told 7NEWS that the materials found inside "were used for chemical labs. Things like Coleman fuel, glassware, hoses and heaters." And the fumes from a Coleman fuel canister and a water heater was all it took to take two lives, police said. "The fumes are heavier than air and they go along the surface of the floor, and they went right to the flame from the water heater," Denver Police Sgt. Mark Olin said. The two survivors, a 47-year-old man and a 28-year-old man, are in police custody while they are being treated at a hospital, 7NEWS reported. Their names have not been released pending official charges. "This is the first lab we found with a fire and a death involved," Olin said. "It is just beside me that people choose to do this, knowing the dangers behind it." Neighbors in the area, who were unknowlingly put in danger, were shocked with the discovery. "They kept to themselves pretty much. And it was always some kind of activity there, so you're kinda suspicious, but you don't expect it," neighbor Tony Luci said. Firefighters were called to the duplex on Lincoln at about 10:30 p.m. on the report of a fire in the basement. When they arrived, they saw a man standing in front of the duplex with minor burns to his hands and feet, 7NEWS reported. He told firefighters that there were more people trapped inside the home. When firefighters stormed in, they found another man with significant burn injuries. He was transported to University of Colorado Health Sciences Center, where he was listed in fair condition with second-degree burns to his hands and feet, 7NEWS reported. After the smoke cleared and the blaze was out, firefighters found the bodies of two women in a crawl space adjacent to the basement level of the home. The victims' names were not released, but the women appeared to be in their 20s, fire officials said. Their causes of death will be released, pending autopsies scheduled for Jan. 17. Police said that is the third meth lab uncovered in the past five days, and the second one that has resulted in fire.