– Another game-changer? One of the United Nations' chief investigators says evidence is building that sarin gas was used in the Syrian conflict—but by rebels, not Bashar al-Assad's regime. "Our investigators have been in neighboring countries interviewing victims, doctors, and field hospitals" and "there are strong, concrete suspicions but not yet incontrovertible proof of the use of sarin gas," said Carla Del Ponte, a member of a panel probing alleged Syrian war crimes, Reuters reports. "This was use on the part of the opposition, the rebels, not by the government authorities," she adds. The war crimes inquiry commission Del Ponte is involved with is separate from the main UN probe into chemical weapons use in Syria. Each side accused the other of using chemical weapons during fighting in Aleppo in March, while Britain and France say they have evidence that regime forces used nerve agents in attacks on rebels. In other developments: Israeli airstrikes on targets inside Syria in recent days have killed at least 42 government soldiers, the Syrian Observatory for Human Rights tells the AP. Israel today emphasized that the strikes were not meant to aid rebels, Reuters adds, but rather to block weapons from Hezbollah. The Israeli move renewed debate on whether the US should use airstrikes against the Assad regime, the New York Times reports. John McCain, who yesterday blasted President Obama's "red line" as being "written in disappearing ink," said the strikes show that Syria's air defense system may not be much of an obstacle. Opposition activists say rebel forces shot down a military helicopter last night, killing eight government troops, the AP reports. The regime's air power has long been a chief target of rebels and activists say rebels also attacked and occupied parts of an air base in the north of the country yesterday, killing the base's commander and capturing a tank unit.