It's been horrible watching the conflict in Syria unfold particularly the recent chemical weapons attacks.
The UN is investigating the evidence taken from the scene. It's essential that everyone can agree the results are independent and reliable.
Labs all over the world are being used and dummy samples are being mixed in with the real ones to make sure the labs are getting reliable results.
As with all such investigations the results won't be 100% certain. But without this level of scientific scrutiny the world's politicians couldn't possibly hope to make an informed decision about what to do next.