UNITED NATIONS -- The leader of the chemical weapons inspection team that verified the use of sarin gas in five instances during the nearly three-year civil war in Syria said he can't answer a critical question: Who launched the attacks?
"It's very difficult to go from where we are," said Ake Sellstrom at a news conference at UN headquarters in Manhattan on Friday. "Using the same information, I would not be able to pinpoint who is the perpetrator. I would not be able to say that. You have to have more intrusive methods."
Putting a finger on who is responsible is difficult for Sellstrom's team even though inspectors were in the country in August during an attack that killed as many as 1,400 men women and children outside of Damascus, Syria's capital.
Sellstrom was among a panel of experts who spoke at the UN a day after the release of an 82-page final report on Thursday that confirmed the use of sarin gas in five instances over the course of the war.
"The United Nations Mission collected clear and convincing evidence that chemical weapons were used also against civilians, including children, on a relatively large scale in the Ghouta area of Damascus on 21 August 2013," the report said.
The panel also included Angela Kane, UN high representative for Disarmament Affairs, Scott Cairns of the Organization for the Prohibition of Chemical Weapons and Dr. Maurizio Barbeschi of the World Health Organization.
U.S. and Syrian officials could not be reached for comment.
Sellstrom, who led the joint UN-OPCW team, added that, though he believes his team performed a stellar job, grading it at least an 8.7 out 10, he said their evidence would not hold up in a court to prosecute someone for war crimes.
He said that anyone who hopes to pursue a criminal case against an alleged attacker would need the evidence his team has amassed as well as other "more intrusive methods."
In the wake of the August attack and since, world leaders including President Barack Obama and UN Secretary-General Ban Ki-moon, called for the perpetrators of the attack to be held accountable.
U.S. officials have insisted that Syrian President Bashar Assad's military is responsible, at least for the Aug. 21 attack in Ghouta, outside of Damascus.
Obama had called the use of chemical weapons a "red line" that, once crossed, could trigger a military response from the United States.
Obama adopted a softer stance as Russia stepped in and helped broker an agreement that allowed for the UN-supervised destruction of Syria's stockpile of chemical weapons, a process that has begun and with which officials have said Syria has complied.
The August attack occurred as Sellstrom's team had arrived in the country to examine other sites where either the Syrian government or other countries, such as France and Britain, had said were sites of chemical weapons attacks. Syria itself was the first to report the attack in Khan al-Assal in March.
The team came under sniper fire when it tried to travel to Ghouta to collect samples for inspection, but no one was injured and the team returned later to work after the gunfire subsided.
The report said that chemical weapons had almost definitely been used in Ghouta, but the results were less definitive in Khan al-Assal, Jobar, Saraqeb and Ashrafieh Sahnaya. The inspectors were unable to visit some of the sites, which may not have retained ample quantities of sarin gas several months since any attack.
The report also could not say for sure whether it had been used in Bahhariyeh and Sheik Maqsoud.
After release of the report Thursday, Ban on Friday said someone must be responsible for the attacks.
"The international community has a moral and political responsibility to hold accountable those responsible, to deter future incidents and to ensure that chemical weapons can never re-emerge as an instrument of warfare," he told the General Assembly.
Ban is scheduled to brief the Security Council on the report on Monday.