Well, try reading the Reuters analysis, which includes reference to the UN reports:  http:www.reuters.com/article/us-syria-idUSKCN10Z2KY

Remember that the Russians brokered the supposed Syrian surrender of  all its chemical weapons.  The UN formally approved that deal, with the proviso that any further use of chemical weapons would involve UN-approved sanctions.  Russia supported that vote.  When Syria then turned around and used chlorine (against rebels and civilians alike) on multiple occasions ( reports cited in the Reuters article), Russia blocked imposition of UN sanctions with its Security Council veto. 

Read the reports and not the misrepresentations about those reports.