A man was arrested on Thursday in the FBI's nearly 5-year-old investigation into pipe bombs placed outside the headquarters of the Republican and Democratic national parties in Washington on the eve of the Jan. 6, 2021, riot at the Capitol and has been charged with an explosives offense, prosecutors said.

The arrest marks the first time investigators have identified a suspect in an act that had long vexed law enforcement, spawned a multitude of conspiracy theories and remained an enduring mystery in the shadow of the dark chapter of American history that is the violent Capitol siege.

The suspect in custody has been identified as Brian Cole Jr., according to Attorney General Pam Bondi. He has been charged with the use of an explosive device, and more charges are possible as part of the ongoing investigation.

Calls to relatives of Cole listed in public records were not immediately returned on Thursday. Hours after Cole was taken into custody, unmarked law enforcement vehicles lined the Virginia cul-de-sac where Cole’s home is while FBI agents helped shoo away onlookers. Authorities were seen entering the house and examining the trunk of a car nearby.