The men charged with protecting the Capitol conferred early on the Washington Navy Yard shooting, but their jurisdictional decisions on Monday show they came to different conclusions on how to proceed.

Senate Sergeant-at-Arms Terrance Gainer told CQ Roll Call on Tuesday that, in retrospect, his decision to lock down did not seem necessary, but he did so to not take any chances and to conform with the best law enforcement practices.

But the decision of House Sergeant-at-Arms Paul Irving not to lock down the House created an awkward situation.

“It would have been more effective and less troublesome to the police as well as to optics in general if the House had taken a similar course of action,” Gainer said. “Reasonable professionals disagreed. I respect Mr. Irving’s perspective but called it differently. I will avoid that in the future and will work with my House counterpart to avoid such situations.”

Gainer said the lockdown had limited effectiveness “but served its purpose in the Senate buildings, page dorm and Senate day care.”

Shots were first reported shortly after 8:15 a.m. Monday at the Naval Sea Systems Command at the Navy Yard’s Building 197, about 1.5 miles southeast of the Capitol.

At 8:54 a.m., Capitol Police reported that several units of officers were providing mutual support and assistance to the Metropolitan Police Department. At the time, staffers, employees and reporters were arriving on the Capitol campus greeted by the sight of Capitol Police officers in tactical gear and in increased numbers. The department called the enhanced security a “proactive, precautionary measure related to the active shooter.”

As city officials warned the public of a shelter-in-place order for the Navy Yard area, Capitol Police Chief Kim Dine, Gainer and Irving began talking about potential security concerns on the campus. Gainer, a former Capitol Police chief, told CQ Roll Call that he first consulted with Dine just after 9 a.m.

At 9:13 a.m., Gainer’s official Twitter account sent out its first message on the mass shooting: “RE: #NavyYardShooting: There is no known direct threat to the #USCapitol. But you will see USCP officers taking extra precautions here.”

The Capitol Police sent out a 9:27 a.m. statement reiterating there was “no known direct threat” to the Capitol but said the department would be conducting enhanced security operations. Gainer shared the same information with Senate staff one minute later.

Metro Transit Police briefly closed the New Jersey Avenue entrance to the Navy Yard Metro Station, and city officials continued to warn residents to stay clear. By 9:30 a.m., police had closed the 11th Street Bridge, as well as M Street Southeast between Second and Fourth streets.

By 10:30 a.m., Ronald Reagan Washington National Airport was holding flights. President Barack Obama issued a statement at a prescheduled news conference, and the death toll continued to rise. At that point, the Police Board — consisting of Gainer, Irving, Architect of the Capitol Stephen T. Ayers and Dine, who is an ex-officio member — conducted its first conference call. Personal conversations between its members had been ongoing, Gainer said.

Both chambers were set to convene at 2 p.m., although the House was set only for a pro forma session. Gainer said the Police Board conducted two more conference calls before that, at 11:20 a.m. and 1:30 p.m.

Shortly before the House pro forma session, at 1:30 p.m., Irving sent an email to House staff.

“The facts available from the shootings at the Navy Yard continue to evolve,” he wrote. “Information about additional shooters is yet unclear, and not confirmed. We are evaluating available intelligence and evidence. There is no information indicating the Capitol Complex, staff, visitors or Members are at risk. The USCP has implemented substantial additional security measures. We will keep you apprised of information.”

At 2 p.m., the House convened for its brief pro forma session and adjourned within minutes. The Senate convened and, after brief remarks from Senate Majority Leader Harry Reid, D-Nev., and Minority Leader Mitch McConnell, R-Ky., adjourned.

By this point, shooter Aaron Alexis had been dead for almost five hours. At 2:12 p.m., about 50 minutes before Gainer sent out the order for a Senate lockdown, Metropolitan Police Chief Cathy Lanier said police still had “reason to believe” at least two other men seen carrying firearms could be suspects in the shooting.

But by 2:49 p.m., the office of Paul A. Quander Jr., deputy mayor of the District, tweeted that the white man being sought by authorities had been identified and was not a suspect.

Gainer told CQ Roll Call on Tuesday that he made his announcement to staff that he was ordering a lockdown shortly after 3 p.m., after numerous calls with Dine and Irving, based on the possibility of other shooters being involved in the Navy Yard incident. “I opted, based on experience, to be cautious,” he said.

“Realizing and valuing the professional opinions of others in the community and after looking at the facts as presented to us we saw no compelling reason that required a lockdown or shelter in place at that time,” said House Deputy Sergeant-at-Arms Donald Kellaher.

The Senate lockdown was partially lifted at 4:18 p.m., allowing staff to exit the buildings, but no one other than staff was allowed to enter Senate facilities until Tuesday morning.

Gainer said the length of the lockdown was unknown at the time it was initiated.

“I indicated it would be in effect until I had more information; I lifted it when more complete information became available and the situation at the scene was calming,” he said.

Leaders on the House Administration Committee gave positive assessments of the choices made on Tuesday, with Chairwoman Candice S. Miller, R-Mich., saying officials’ “close coordination made it possible for them to enhance security throughout the complex.” The Senate Rules and Administration Committee did not respond to requests for comment. Dine declined to speak about the timeline or the lockdown.