LONDON - British counter-terrorism police are helping the investigation of what caused the illness of former Russian double agent Sergei Skripal, Britain's top counter-terrorism officer said on Tuesday.The 66-year-old former spy and a 33-year-old woman who was known to him were found unconscious on a bench in a shopping centre on Sunday in the English city of Salisbury after exposure to what police said was an unknown substance."It's a very unusual case and the critical thing is to get to the bottom of what's caused these illnesses as quickly as possible," Rowley told BBC radio."If necessary we will bring we will bring that investigation into the counter-terrorism network. We're doing all the things you would expect us to do, we're speaking to witnesses, we're taking forensic samples at the scene, we're doing toxicology work and that will help us to get to an answer. I can't say any more at this stage," Rowley said.