Did Turkey stage the sarin attack in Syria?

[Raphael]

This is what investigative reporter Seymour Hersh is arguing. He wrote a very long piece about it in the London Review of Books:

Seymour M. Hersh · The Red Line and the Rat Line · LRB 6 April 2014

Summary:

In a lengthy article published Sunday by the London Review of Books, investigative journalist Seymour Hersh reports that the sarin gas attack on a Damascus suburb on August 21, 2013 was actually carried out by Syrian “rebel” forces acting at the behest of Turkey, for the purpose of providing a pretext for a US attack on Syria.
New exposé by Seymour Hersh: Turkey staged gas attack to provoke US war on Syria - World Socialist Web Site