Police found the body of Edward Henderson, 52, Wednesday inside the building located at 6608 South Bishop. The medical examiner ruled he died of carbon monoxide poisoning.
Two other men were taken to the hospital. The extent of their injuries is unknown.
Saturday, Lydia Watkins, 42, died in the same building. Tests showed she also had high levels of carbon monoxide in her blood.
Officials say a faulty boiler may be to blame.
Neighbors of the victims are stunned.
"That's really tragic. That's really sad," said Wendell Peoples.
"It's really kind of sad that both died. It's just a shame," said Destinee West.
After Watkins died, Peoples Gas said an inspection revealed a faulty water heater and boiler. The company said it disconnected the appliances, capped off their connectors and attached notices saying they needed fixing before being reconnected.
"By disconnecting these and tagging them, we felt like we were giving a clear signal that these appliances were in need of repair," said Bonnie Johnson, Peoples Gas spokesperson.
But Peoples Gas said someone reconnected the appliances, and on Wednesday police found the body of Edward Henderson.
A childhood friend of Henderson's said the 52-year-old had lived on the block for decades and that the home had been in his family since the 1960s.
"They were very kind, you know, very nice neighbors. They always spoke when you came out and they saw you. They were very nice," said neighbor Ethel Patterson.
"It was very shocking to hear of anything like that, especially two, two fatal incidents. That's really shocking to me," said Denyse Peoples, another neighbor.
It's unclear if the home had working carbon monoxide detectors. But neighbors say they're making sure their homes do.
"I spoke to my landlord about it. We have a working carbon monoxide detector and smoke detector," said Peoples.
The gas has now been shut off to the home entirely as police investigate these two deaths.