WASHINGTON (NewsNation Now) — 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 President Donald Trump’s 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.

Police said 52 people were arrested as of Wednesday night, including 26 on the Capitol grounds. Fourteen police officers were injured, Contee said.

Rep. Zoe Lofgren, D-Calif., chairwoman of the House Administration Committee, said the breach “raises grave security concerns,″ adding that her committee will work with House and Senate leaders to review the police response — and its preparedness.

National security expert JJ Green spoke to NewsNation about the potential global ramifications of the breach.

“The message this sends to the international community is, ‘Am I safe when I go to the U.S. Congress? Am I safe when I go to Washington?” Green said. “There are lots of questions that the people that I know overseas are having and floating. They are watching in horror.”

Lawmakers crouched under desks and donned gas masks while police futilely tried to barricade the building when people marched to the Capitol from a rally near the White House in support of President Donald Trump. Washington’s mayor instituted an evening curfew in an attempt to contain the violence.

The mob broke windows, entered both the Senate and House chambers and went into the offices of lawmakers, including House Speaker Nancy Pelosi, D-Calif.

“It won’t be anything that will soon be forgotten, and certainly from a police and law enforcement point of view, the question running through everyone’s mind is ‘How could this happen?'” Green said. “This has been a very strange day, a very tragic day, a deadly day that no one will forget any time soon.”

You can watch Green’s full interview in the player above.