A man charged in a string of shootings near Atlanta that left three people dead, including a Department of Homeland Security employee who was walking her dog, died in jail Tuesday night, authorities said. Olaolukitan Adon Abel, 26, was found in his cell unresponsive, according to a statement from the DeKalb County Sheriff's Office. Officials performed lifesaving measures on the US Navy veteran, but he was later pronounced dead, the AP reports. "There is no indication of criminal activity or foul play," the sheriff's office said. Deputy Chief Investigator Jess Dillar tells CNN that the death is being investigated but it "will take some time, as we need a lot more information before we make a determination."