Police were stationed in building Trump gunman shot from

An FBI agent is seen near the building used to shoot at Trump

Police were stationed inside the building from which gunman Thomas Matthew Crooks fired shots at Donald Trump, the director of the US Secret Service Kimberly Cheatle says.

Ms Cheatle told ABC News that local police were inside the building while Crooks was on the roof, and that local police - not the Secret Service - had been “responsible" for securing the building and its outer perimeter.

Questions have swirled about how police officers and agents tasked with securing Trump's Pennsylvania rally allowed Crooks to get as close as he did.

He was able to access the roof of a building near the outdoor event at Butler County fairgrounds, Pennsylvania, from where he shot at Trump 130m (430ft) away.

The local police deployment inside the building comprised three snipers, who are alleged to have seen Crooks trying to get on the roof, according to sources quoted by CBS News, the BBC's US partner.

One audience member was killed and two others critically injured in the shooting. Trump was wounded in the ear.

Secret Service spokesman Anthony Guglielmi said that his agency was responsible for securing inside the perimeter of the fairgrounds, while local police secured the area outside, which included the private building used by the gunman.

The local sheriff's department referred BBC questions to the state police, which said it was not responsible for the area containing the building.

A state police spokesman told the BBC that it provided "all resources" requested by the Secret Service, including between 30 to 40 troopers inside the perimeter.

Many observers have questioned how security plans broke down to allow the gunman unobstructed access to Trump.

Crowd members said they had spotted the suspect on the roof minutes before the shooting started, while Butler County Sheriff Michael Slupe said a local security officer had also spotted him but could not stop him.

The sheriff admitted there had been "a failure" in securing the premises, but said he believed that there was no single party to blame.

After Trump arrived at the venue, officers were alerted about a suspicious man near the building but searched and did not spot him.

A local officer with the Butler Township Police Department attempted to check the roof. He was hoisted up by another officer when he "made visual contact with an individual who pointed a rifle at him", Butler Township Manager Tom Knights told CBS.

The officer was in a "defenceless position" and couldn't engage the suspect, Mr Knights said. The officer "let go and fell to the ground" then immediately alerted others to the armed suspect's location.

Moments later the shooting began.

Secret Service agents escorted Trump off the stage after shots rang out

It is common for the US Secret Service to rely on local police for help when securing rallies, said Jason Russell, founder of Secure Environments Consultants who worked as an agent from 2002 to 2010, including during election campaigns.

“The Secret Service doesn’t have unlimited resources in terms of agents that they can post everywhere,” he told the BBC.

He said that agents usually scope out a campaign event’s venue days in advance to develop a security plan that is then shared with local police agencies.

During an event, he said communications were shared with every agency involved. However, he added that in "the 10 seconds that it takes" for information to flow through, that could be just enough time for a gunman to fire a few shots.

The rooftop was a known vulnerability before the event, according to NBC News, which cited two sources familiar with Secret Service operations.

Mr Russell said it was probable that Secret Service agents identified that building as a threat, and had requested local authorities to station officers nearby to prevent access.

“For whatever reason, that didn’t happen,” he said.

One witness, Thomas Gleason, who served 21 years with the US Army as paratrooper and ranger, said "there should have been greater security for a long-range threat".

"Looking at the distance and vantage point, if someone is going to try to assassinate [Trump] that would have been the most logical shooting point," he said.

The FBI has since taken over the role of lead investigator into the incident, and the shooting is now the subject of several other investigations by both the House and the Senate.

Secretary of Homeland Security Alejandro Mayorkas called it a “failure” of security, telling CNN that "an incident like this cannot happen again".

Ms Cheatle said on Monday that her agency is working with federal and local police to "understand what happened, how it happened, and how we can prevent an incident like this from taking place again".

"The buck stops with me," she said in the ABC interview, adding that she would not step down in the face of mounting calls from some lawmakers.

A briefing for Senators on 17 July left many questions unanswered, with Senator Ron Johnson describing the call as "unbelievably uninformative", with only four questions permitted.

John Barrasso, a Wyoming Republican, told CBS that the senators were told Crooks was identified well before the attack and he was found carrying a range finder and a backpack.

"The Secret Service lost sight of him," he added. "No one has taken responsibility. No one has been held responsible."

Ms Cheatle has been subpoenaed to face the House Committee on Oversight and Accountability on 22 July.

Republicans on the committee have also called on the Secret Service to produce evidence including internal communications, audio and video recordings, messages to local law enforcement, maps, diagrams and pre-event assessments.

Additionally, House Speaker Mike Johnson has said that a bipartisan task force will be assembled to investigate the assassination attempt and concerns about how security was handled.