Columbia, SC – South Carolina authorities say two people found dead in separate apartments in the same building may have been killed by natural gas fumes or carbon monoxide.

Columbia Police Chief Skip Holbrook said autopsy results and testing will be needed to confirm what caused the deaths. But he says there was no sign of violence.

Holbrook said at a news conference the first body was found Thursday morning by an apartment complex worker checking on someone who didn’t make it into work. Authorities checking other apartments in the building then found the second victim.

Columbia Fire Chief Aubrey Jenkins says firefighters did not find lethal levels of gas or carbon monoxide in the apartments, but the poisonous gas could have dispersed as crews tried to save the victims.