"Today, around 100 counter-terrorism officers remain in Salisbury. They continue to sift through and assess all the available evidence and are following every possible lead to identifying those responsible," the police said.
According to the police, the police have undertaken 176 churches and taken over 900 witness statements.
The investigation is focused on Skripals' home, where the specialist found the nerve agent in high concentration. Its traces were found in other locations as well but in lower concentrations.
"Clearly this is a very unusual case – both in its scale and complexity. We have said from the start that this investigation was going to take some time as we rigorously follow the evidence," Deputy Assistant Commissioner Dean Haydon, the Senior National Coordinator for Counter Terrorism Policing, said, as quoted in a press statement.
The United Kingdom and its allies have accused Moscow of having orchestrated the attack with what UK experts claim was the A234 nerve agent, although the accusation has not been substantiated. Russian authorities have strongly refuted the allegations as groundless.