(CNN) -- A man held by Tunisian authorities in connection with the deadly September attack on a U.S. consulate in Libya has been released by a judge, Tunisia's state news agency reported Tuesday.
Ali Harzi was freed Monday by the investigating judge overseeing the case, the TAP news agency reported, citing "an authorized source of the Justice Ministry." He had been arrested in Turkey in connection with the attack that killed the U.S. ambassador to Libya, Christopher Stevens, and three other Americans.
In Washington, U.S. State Department spokeswoman Victoria Nuland referred questions to the FBI, which she said "has the lead on the Benghazi investigation."
TAP reported that Harzi had been questioned by Tunisian authorities and the FBI "as a witness and not a suspect."
But a U.S. federal law enforcement official with direct knowledge of the Benghazi investigation said the freed man remains a suspect.
The fact that Harzi's been freed from detention "doesn't mean he's any less a suspect," the official said, adding Harzi does not appear on video taken of the Benghazi compound.
Investigators have identified at least 15 individuals that "we're taking a serious look at," the official told CNN, indicating some of them were identified on the video.
Ultimately, the official said, "we will get indictments, but it's not possible to put a timetable on it."
An independent review released in December found that "systemic failures and leadership and management deficiencies" at the State Department left security at the Benghazi consulate "grossly inadequate" when suspected Islamic militants attacked the American mission on September 11.
A State Department official in charge of diplomatic security resigned after the report came out, and three others have been placed on administrative leave.
Nuland said Tuesday there has been no decision about whether to reopen the consulate in Benghazi, the cradle of the 2011 revolution that drove longtime Libyan strongman Moammar Gadhafi from power.
"Obviously, we are in touch with Libyan officials on all aspects of safety and security of our diplomatic facility, of our own posture there," she said. "As you know, for many months, we've been talking to Libya about our willingness to support efforts that they may have on their own, strengthening their own internal security structures on the police side, on integrating militias -- all those kinds of things. They have not yet availed themselves to some of these offers that we have made."
The attack also sparked a domestic political battle for the Obama administration, which initially attributed the attack to Muslim anger over an anti-Islamic video that sparked violent demonstrations in neighboring Egypt and other countries. U.N. Ambassador Susan Rice came under intense criticism from Republicans in Congress for delivering that account on U.S. news shows in the days after the attack and withdrew her name from contention for secretary of state in a second Obama term as a result.
Rice said her comments were based on declassified talking points, and sources within the intelligence community said the talking points were not modified by any other body, such as the White House.
Sen. Lindsey Graham, R-South Carolina, announced Tuesday that he would oppose the confirmation of John Brennan, President Barack Obama's pick for CIA director, "until our questions are answered."
"This ever-changing story should be resolved," Graham said in a statement issued by his office. "It is imperative we understand who changed the talking points just weeks before a presidential election and why. The stonewalling on Benghazi by the Obama administration must come to an end."
White House spokesman Jay Carney told reporters later that the administration is working to hunt down the attackers and improve security at U.S. missions, dismissing what he called "the essential irrelevance" of the controversy over Rice's comments.
"The president is focused on those issues, not what seems to be the continued political fascination with appearances on Sunday shows," Carney said.
CNN's Susan Candiotti contributed to this report.