Members of a bipartisan House taskforce investigating the assassination attempts on former US president Donald Trump has emphasised that the Secret Service was responsible for the failures in planning and communication, not local authorities.

Mr Trump was wounded and one man was killed when a gunman opened fire at a rally in Butler, Pennsylvania.

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Chairman Mike Kelly, leads the first public hearing of a bipartisan congressional taskforce investigating the assassination attempts against former President Donald Trump (Rod Lamkey JR/AP)

Officials repeatedly questioned why the agency tasked with protecting the country’s top leaders did not do a better job communicating with local authorities during the July 13 rally, particularly when it came to securing the building that was widely agreed to be a security threat but was left so unprotected that gunman Thomas Michael Crooks was able to climb up and open fire on Mr Trump.

The Republican co-chairman of the committee, Mike Kelly from Pennsylvania, said: “In the days leading up to the rally, it was not a single mistake that allowed Crooks to outmanoeuvre one of our country’s most elite group of security professionals, there were security failures on multiple fronts.”

Jason Crow, praised local law enforcement but added: “It is also clear, however, that the communication between the Secret Service and local and state partners was disjointed and unclear.”

The panel — comprised of seven Republicans and six Democrats — has spent the last two months analysing the security failures at the rally, conducting nearly two dozen interviews with law enforcement and receiving more than 2,800 pages of documents from the Secret Service.

The hearing on Thursday largely focused on the rally shooting with testimony from Pennsylvania and Butler County police officials.

The Secret Service often relies on local authorities to secure bigger events where protected people like Mr Trump appear around the country. But following the attempt, the agency was heavily criticised for failing to clearly communicate what it needed from those local agencies that day.

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From left, Sgt Edward Lenz, Commander of Butler County Emergency Services Unit, Patrolman Drew Blasko of Butler Township Police Dept, Lt John Herold of Pennsylvania State Police, and former US Secret Service agent Patrick Sullivan, were among those to give evidence at the first public hearing (Ben Curtis/AP)

One key question has been why there were no law enforcement personnel on top of the AGR building where Crooks eventually climbed up and took his shots, considering that it was so close to the rally stage and afforded a clear line of sight to Mr Trump.

Edward Lenz, commander for the Butler County Emergency Services Unit who was in charge of the local tactical units operating at the Butler rally, said his agency was never asked to put a sniper team on top of the roof and never said that they would.

Mr Lenz said the Secret Service knew their shooters were inside the AGR Building and there was no “feedback or guidance” from the Secret Service that they wanted the team anywhere else.

“They knew where we would be,” Mr Lenz said. “They knew what our plan was.”

Mr Lenz also said that Secret Service officials did not check with him or his team to make sure they were in place before Mr Trump went on stage and that the emergency communication for July 13 had not been worked out in advance.

Drew Blasko, an assistant team leader of the sniper unit within the Butler Township Emergency Services Unit, said that he shared his concerns about the building with the Secret Service ahead of the rally and said his team did not have the manpower to post anyone there.

He said he asked the Secret Service that additional people be posted there and was told “that they would take care of it”.

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Chairman Mike Kelly speaks in front of a site map at the first public hearing of a bipartisan congressional task force investigating the assassination attempts against Donald Trump (Ben Curtis/AP)

Some of the witnesses also said that there had been discussions ahead of time about using opaque screens or large farm equipment to block the line of sight to the stage, but it is not clear what happened to those suggestions.

Officials struggled to get witnesses to zero in on a single individual or moment that led to the assassination attempt.

Local police officials and a retired Secret Service agent also giving evidence instead pointed to a series of incidents and mistakes that ultimately allowed Crooks to remain undeterred for a prolonged period of time and eventually take his shot at the former president.

“Communication was totally lacking here,” said Lou Correa, a Democrat from California. “What went wrong? Who’s in charge?”

Thursday’s session was the fourth congressional hearing about the Butler shooting since July.

Secret Service Director Kimberly Cheatle resigned one day after she appeared before a congressional hearing where she was berated for hours by both Democrats and Republicans for the agency’s security failures.

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The former director of the Secret Service said that the attempt on Donald Trump’s life was the service’s ‘most significant operational failure’ in decades (Evan Vucci/AP)

Ms Cheatle called the Pennsylvania attempt on Mr Trump’s life the Secret Service’s “most significant operational failure” in decades, but she angered officials by failing to answer specific questions about the investigation.

An interim report from the Senate Homeland Security and Governmental Affairs Committee, which is also conducting an investigation, said the Secret Service failed to give clear instructions on how state and local officials should cover the building where the gunman eventually took up position.

The report also said the agency did not make sure it could share information with local partners in real-time.

The House panel is expected to propose a series of legislative reforms and issue its own final report before December 13.