Former top US health official Anthony Fauci invoked the Fifth Amendment during a hearing before a Republican-led Senate committee about the origins of the Covid-19 pandemic.

The amendment to the US Constitution states that no individual can be “compelled in any criminal case to be a witness against himself”.

Fauci’s refusal to answer questions came at the beginning of the hearing on Wednesday, days after Republican Senator Rand Paul released Fauci writings in which he mused about his fame and the origins of Covid.

Fauci, who led the National Institute of Allergy and Infectious Diseases (NIAID), said Paul’s release of his diary entries was one reason he would not answer senators’ questions.

“Although it pains me to do so because of the respect I have for the legislative branch of government … under the advice of my attorneys, I will invoke my right under the Fifth Amendment of the constitution to refrain from answering your questions,” Fauci said.

Taking the Fifth is not an admission of guilt – it is designed to protect individuals against coercion, mistakes, and unfair burden-shifting.

Fauci noted that he had previously testified under oath before several congressional committees, but he asserted that Paul has an “obvious obsession” with pushing for Fauci to be prosecuted had led him not to answer questions this time.

“The only conclusion I can reach is that the sole reason he is calling me before this committee is to get me to say something – anything – that could vindicate his repeated public pledges that I end up, in his words, ‘behind bars,'” Fauci said.

Paul continued questioning Fauci despite his refusal to answer. The hearing grew tense at times, including when one of Fauci’s lawyers who was seated next to him repeatedly tried to interject during Paul’s questioning. Paul directed a security guard to remove him from the room.

During opening remarks, Paul claimed Fauci’s diary entries contradicted what he told the American people about the origins of the virus.

Paul suggested that while Fauci said publicly that Covid originated naturally, he privately believed the virus originated in a medical lab. The senator has repeatedly promoted the lab-leak theory that Covid came from China’s Wuhan Institute of Virology.

Many scientists favour a theory of “animal spillover”, meaning the virus began when an animal carrying the virus infected a human. However, scientists and evidence have not definitively coalesced around either theory.

Fauci’s diary entries reflect openness at the start of the pandemic to two possible theories about Covid’s origins – including natural origins and a lab leak – before he appears to become more convinced it had a natural origin.