The man accused of carrying out a deadly string of seemingly random shootings in the Atlanta suburbs, including the killing of a Department of Homeland Security employee walking her dog, has died in jail before authorities could determine a motive.

Olaolukitan Adon Abel, 26, was discovered unresponsive in his cell at approximately 6:48 p.m. at the DeKalb County Jail. Officials attempted lifesaving measures, but he was pronounced dead about a half hour later, the sheriff’s office said.

“There is no indication of criminal activity or foul play,” a statement from the sheriff’s office said, adding that the medical examiner’s office will determine an official cause of death. The sheriff’s office said it is conducting an internal review of the death, in accordance with agency policy.

Adon Abel had been charged in connection with last week’s shootings, which killed Prianna Weathers, 31, and Lauren Bullis, 40, a DHS auditor. Prosecutors were also pursuing an additional murder charge after Tony Mathews, 49, who was wounded in the attack, died Sunday.

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Investigators have not identified a motive and said it remains unclear whether the suspect knew any of the victims. Police believe at least one of the attacks may have been random.

Roommates told The Associated Press that shortly before the shootings, Adon Abel argued over the air conditioning at their shared home and stormed out.

The timeline of the terror began at approximately 12:50 a.m. April 13, when DeKalb County Police discovered Weathers shot multiple times in the Decatur area.

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The violence then shifted to Brookhaven, where Mathews was ambushed and shot several times outside a business center.

The spree reached a horrific conclusion around 6:50 a.m. in Panthersville, a community south of Decatur, where Bullis was found both shot and stabbed. Witnesses, police said, reported seeing a man standing over her before he fled the scene.

DHS Secretary Markwayne Mullin confirmed Wednesday that Bullis was “brutally shot and stabbed to death,” identifying the suspect as Adon Abel, who was naturalized in 2022 and had a record that included convictions for sexual battery, assault and battery against a police officer.

Adon Abel, originally from the United Kingdom, became a U.S. citizen in 2022 while serving in the Navy in San Diego.

The case has raised new questions about the federal government’s vetting process after DHS recently acknowledged significant screening gaps under former President Joe Biden.

Fox News Digital’s Sarah Rumpf-Whitten and Peter Pinedo, along with The Associated Press, contributed to this report.