Chicago police are trying to alert potential drug users in the South Austin and West Garfield Park neighborhoods about an unusually pure batch of heroin they believe is responsible for killing two people and sickening at least four others.

Monday night around 10 p.m., a 35-year-old black male was found dead at a hotel on the 4900 block of Madison Street. An hour earlier, a 21-year-old white male was found dead on the 500 block of South State Street. Police spokesperson Patrice Harper said Wednesday that investigators are still awaiting word from the Cook County Medical Examiner confirming the cause of death in both cases.

The night before, Sept. 5, police had received numerous 911 calls regarding women passed out in the street in the 4600 and 4800 blocks of West Adams and the 4900 block of West Madison. All four women, say police, report having purchased the heroin between 9 p.m. and 10 p.m. in a 4-block area in West Garfield and South Austin.

According to Harper, three of the women overdose victims were taken to West Suburban Hospital in Oak Park, and one to Loretto Hospital in Chicago. All were treated and eventually released.

Police continue to investigate the source of the heroin.