Skripal poisoning: Two suspects identified by UK police

Detectives in the United Kingdom appear to have isolated two people from CCTV images as their prime suspects in the nerve agent poisoning of Sergei and Yulia Skripal in March. The attack lead to the subsequent death of Dawn Sturgess, and the accidental contamination of her partner Charlie Rowley. The police have yet to confirm any progress to the public at this stage. The BBC's security correspondent is Frank Gardner. He talks to Susie Ferguson.