Police in the UK say they believe former Russian spy Sergei Skripal and his daughter Yulia were poisoned at their home.
The pair were found unconscious on a bench in Salisbury on March 4th.
Sergei (66) and Yulia (33) remain in a critical but stable condition in hospital, which officials saying a nerve agent was used in the attack.
In an update this evening, Met Police said forensic tests show the highest concentration discovered so far has been on the front door of the Skripals' home.
Deputy Assistant Commissioner Dean Haydon said: "At this point in our investigation, we believe the Skripals first came into contact with the nerve agent from their front door. We are therefore focusing much of our efforts in and around their address.
"Those living in the Skripals’ neighbourhood can expect to see officers carrying out searches as part of this but I want to reassure them that the risk remains low and our searches are precautionary."
Around 250 counter-terrorism detectives are working on the investigation, and police say enquiries around the Skripals' home will continue for weeks and possibly months.
Investigators are said to be trawling through 5,000 hours of CCTV footage, and have identified 500 witnesses.
The British government has accused Russia of being responsible for the attack, a claim the Kremlin has repeatedly denied.
Around two dozen countries - including Ireland - have this week expelled Russian diplomats in solidarity with the UK, with the Kremlin pledging a 'mirror-like' response.
Earlier today, the Russian foreign ministry claimed there was a "possible involvement of the UK intelligence services" in the attack, and demanded "convincing proof of the opposite".