Experts hunt for traces of nerve agent in bid to track Skripals' attacker

Impurities found in nerve agent may be key to identifying where it was made - if experts can locate a pure sample

Forensic experts will be looking for traces of nerve agent on the clothes of Sergei Skripal and his daughter, Yulia, and in the area where the two were attacked, in an effort to track down where the deadly substance was made, researchers say.

Related: Russian spy attack: police officer left ill named as DS Nick Bailey