Investigators now think Sergei Skripal and his daughter came into contact with a nerve agent at Skripal's front door.

British investigators found the  highest concentration  of the nerve agent right in front of Skripal's Salisbury home.

He and his daughter were later found unresponsive on a park bench.

They remain in critical condition.

Skripal's niece said in  an interview  she has little hope her two relatives will survive.