Lt. Col. Andy Wood, a Utah National Guard Army Green Beret who was the top security official at the United States consulate in Libya, has been subpoenaed by congressional investigators for an upcoming hearing on the deadly Benghazi attacks last month.

Wood headed a site security team in Libya. He is among three witnesses who will speak at Wednesday's hearing.

Wood told CBS News and congressional investigators that his 16-member team and a State Department force left Libya in August despite U.S. officials in Libya asking for increased security.

Other witnesses are Charlene Lamb, deputy assistant secretary for international programs at the Bureau of Diplomat Security at the U.S. Department of State, and Eric Nordstrom, a regional security officer, also from the State Department.

The hearing is an effort to garner more details about what happened last month when the compound was attacked.

The Sept. 11 attack in Libya, which is believed to be an act of terrorism involving al Qaida affiliates, killed four Americans, including Ambassador Chris Stevens. Since then, the security of U.S. diplomatic missions overseas has been called into question with Republicans leading the charge.

The House Committee on Oversight and Government Reform, chaired by Republican Rep. Darrell Issa, has been conducting its own investigation into the safety of the Benghazi consulate. Sources said to be familiar with the Libya operation told lawmakers that 13 threats were made in the six months leading up to the Benghazi incident, with repeated requests made for additional security that were denied.

Officials released conflicting reports shortly after the incident, saying that it was an escalation of the protest against the anti-Island film “Innocence of Muslims.” However, the administration later said it was a pre-planned attack with Secretary of State Hillary Clinton admitting terrorists were involved.

While the FBI continues its investigation, Clinton has agreed to comply with lawmakers to find out what took place that day.

“There are continuing questions about what exactly happened in Benghazi on that night three weeks ago,” she said last week. “And we will not rest until we answer those questions and until we track down the terrorists who killed our people. Active efforts are also under way to determine who was responsible and bring them to justice.”

“No one wants to determine what happened that night in Benghazi more than the President and I do,” she added. “No one is more committed to ensuring it doesn’t happen again. And nobody will hold this Department more accountable than we hold ourselves, because we served with and we knew the four men we lost. They are not just names or profiles to us. They are our colleagues and our friends.”