Rep. John Shimkus (R-Ill.) confirmed Thursday afternoon that two staffers from his office sparked the hours-long lockdown of the Cannon House Office Building after bringing a toy gun through a magnetometer.

“Given initial reports of a male intruder, my staffers were not aware of their involvement,” Shimkus said. “When the description of the female was released, they came forward. We immediately contacted Capitol Police, and the issue was resolved.”

The Capitol Police initially indicated they were looking for a man, after officers spotted what appeared to be a gun in a backpack as it passed through the X-ray machine at the building’s southeast entrance checkpoint. By the time the officer saw the item, the man had left the area, prompting police to search for an individual of that description. After immediate reviews of surveillance video, Capitol Police officials also put out a description of a female suspect. The incident prompted the House to recess.

“The staffers wish to convey their deepest regrets to all Members, fellow staff and visitors to Washington who were inconvenienced by this incident,” read the statement, which did not identify the staffers by name. A spokesman for Shimkus said the office doesn’t plan to name the women.

Capitol Police Chief Terrance Gainer said, depending on the owner’s intent, it is illegal to bring fake weapons into Congressional buildings. During a press conference, he indicated that the police believed there was no ill will, as the toy gun was apparently part of a Halloween costume.

“This was an unfortunate misunderstanding, as a result of my staff’s efforts to put together a Halloween costume during their lunch hour,” Shimkus said. “They did comply with security measures required to enter the building; however, they were caught up in suspicious circumstances surrounding another individual who had entered the building in front of them.”

The Shimkus spokesman said the male who entered in front of them is not a member of Shimkus’ office nor was he accompanying the two women. “The officer misidentified the gun as belonging to the male,” he said, adding that the Congressman does not plan to take any disciplinary action against the two staffers.

House Administration Chairman Bob Ney (R-Ohio) and John Larson (D-Conn.) issued a statement Thursday evening.

“We also commend the brave action of the U.S. Capitol Police Officers who responded immediately and again, put the safety of those on the Capitol campus ahead of their own. We have a great deal of respect for our rank-and-file officers and their response to today’s incident only strengthened this respect and admiration. We also thank all Members and staff for remaining calm and cooperating with security personnel,” the two said.

“Clearly, however, there are some very serious questions that need be addressed surrounding this incident, and we intend to seek answers immediately. This incident will be looked at second-by-second and frame-by-frame to determine how this happened and how it was responded to,” Ney and Larson said.

“We are fully aware of the many concerns that Members, staff, and others have regarding this incident and its aftermath. We share these serious concerns and we will be meeting with House security personnel as soon as possible to determine, among other things, why House offices were not notified more quickly. If mistakes were made, and at this point it appears there were, then those responsible will be held accountable.”