WASHINGTON (AP) — Lawmakers are vowing an investigation into how law enforcement handled Wednesday’s violent breach at the Capitol, questioning whether a lack of preparedness allowed a mob to occupy and vandalize the building.

U.S. Capitol Police, who are charged with protecting Congress, turned to other law enforcement for help with the mob that overwhelmed the complex and sent lawmakers into hiding. Both law enforcement and Trump supporters deployed chemical irritants during the hours long occupation of the complex before it was cleared Wednesday evening.

Four people died, one of them a woman who was shot and killed by police inside the Capitol. Three other people died after suffering “medical emergencies” related to the breach, said Robert Contee, chief of the city’s Metropolitan Police Department.