Police say 52-year-old Develt Bradford was found hanging from his pajamas inside his cell in November at Area 2 police lockup on the Far South Side.
Three days later, 62-year-old Melvin Woods was discovered hanging from his underwear.
"It is our firm belief that an occurrence like that has occurred with these families does not occur in isolation, it does not occur in a vacuum," said family attorney Vivian Tarver-Varnado. "Somewhere, someone is aware of what happened."
While there are cameras in the lockup, the families say they were told nothing was recorded.
The Chicago Police Department says it is assessing its camera system and both cases are under investigation.