March 10 (UPI) -- Britain Home Secretary Amber Rudd on Saturday said police identified more than 200 witnesses have 240 pieces of evidence linked to the nerve agent attack on a former Russian spy and his daughter.
Sergei Skripal, a 66-year-old former colonel in Russia's military intelligence service, and his 33-year-old daughter were found slumped on a bench in a British shopping district Sunday.
The pair are "critical but stable condition," according to Rudd.
A police detective who fell ill after helping the pair remains seriously ill but is awake and able to communicate with his family.
Rudd said it is too early to determine who was behind the poisoning, which is being investigated by more than 250 counter-terrorism police and 180 government soldiers, including chemical warfare experts.
Forensic experts also were seen at the cemetery where Skripal's wife and son were buried. Skripal's wife passed away from cancer in 2012 at the age of 60 and his son died last year, at the age of 43, while in St. Petersburg, Russia.
British officials have said they suspect Moscow might have been behind the attack. On Friday, Russia Foreign Minister Sergey Lavrov rejected that notion.
"We haven't heard a single fact, we only watch reportages on TV where our colleagues say with pathos with serious faces that if this was done by Russia, then the response will be such that Russia will remember it forever," Lavrov said. "This is dishonest, this is pure propaganda, pure fanning of hysterics and hysteria."
Skripal, arrested in Russia in 2006 and convicted of "high treason, was delivered to Britain in 2010 after a spy swap.