London (CNN) Police have identified two suspects in the poisoning of former Russian double agent Sergei Skripal and his daughter Yulia, a source with knowledge of the investigation told CNN on Thursday.

The pair left the UK in the wake of the attack on what is believed to have been a commercial flight, the source added.

Their departure was revealed in a coded Russian message to Moscow sent after the attack, which was intercepted by a British base in Cyprus, the source said. The British government blames the Skripals' poisoning on Russia.

The suspects were identified by UK police, who have been combing through months of surveillance camera footage from UK airports and from Salisbury, the town where the Skripals were poisoned on March 4.

Using facial recognition technology, authorities discovered two "fresh identities" -- individuals not known to have been spies or used in other attacks -- the source added.