WASHINGTON - The chairman of a special House committee investigating the deadly 2012 attacks in Benghazi, Libya, said Wednesday he is "keenly aware" that many people from both parties believe there is nothing left to investigate after a series of congressional and internal reviews, including a House report that found no wrongdoing by Obama administration appointees.

But Rep. Trey Gowdy (R., S.C.) said that "some of those very same folks who now tell us to move on did not believe we should have investigated Benghazi in the first place."

Speaking at the second public hearing of the Benghazi panel, Gowdy said the United States must learn from the past to prevent repeat incidents like the attack that killed the U.S. ambassador and three other Americans.

"We should not move on until there is a complete understanding of how the security environment described by our own government in court documents was allowed to exist," Gowdy said. "We should not move on until there is a complete understanding of why requests for additional security were denied, by whom they were denied and why an ambassador trusted to represent us in a dangerous country was not trusted when he asked for more security."

The 12-member Benghazi panel is reviewing efforts to secure U.S. diplomatic facilities and personnel as it continues investigating the September 2012 attacks that killed U.S. Ambassador Christopher Stevens, foreign service officer Sean Smith, and two CIA contractors, Tyrone S. Woods and Glen Doherty. A Libyan extremist, Ahmed Abu Khatalla, is facing trial on murder charges after he was captured in Libya and taken to the U.S.

House Republicans have called for spending up to $3.3 million on the select committee. Multiple independent, bipartisan and GOP-led inquiries have faulted the State Department for inadequate security, leading to four demotions.