The Russian hitmen accused of poisoning Sergei Skripal have been linked to the plot to assassinate the Montenegrin Prime Minister.
The cover passports of Alexander Petrov and Ruslan Boshirov were issued in the same batch as the passport of Col. Eduard Shishmakov, the GRU officer accused of masterminding the failed coup in October 2016.
The findings suggest that the passports have been issued to aliases by a special authority to a group of military intelligence officers.
Research by the investigative journalist organisation Bellingcat and The Insider Russian has also shown that Petrov traveled extensively through Western Europe before the Novichok attack on Mr Skripal and his daughter Yulia in Salisbury.
It is unclear whether he was accompanied by Boshirov, whose travel data has not been obtained by the group.
Almost as soon as he was issued with his cover passport, Petrov drove to Minsk, in Belarus, before flying to Amsterdam just days after the referendum on Ukraine's EU accession.
Just months later in July 2016 he took a bus into Kazakhstan claiming to officials he was on his way to Beijing, despite the Chinese capital being more than 3,000 miles away. 15 days later he reappears in Tel Aviv, where he catches a flight back to Moscow.
Two months later he uses the passport to fly to the UK for the first time, travelling from Amsterdam to London for less than a week.
He then returns to London in February 2018 and stays for six days - over the same time period that he allegedly poisoned Mr Skripal exactly a year later. The passport was also used to make several trips to Amsterdam, France, Switzerland and Geneva.
The final trip on the cover passport was to London on March 3 this year when the assassination attempt took place.
Petrov and Boshirov, who claim that they were on a long planned holiday, had booked the flight the night before.
Bellingcat also claimed to have been provided information from sources in a Western European law-enforcement agency that the two men had previously been arrested in the Netherlands.
Sources told the Telegraph that they had no record of these arrests taking place.
It has previously been shown that the passport numbers on the alleged hitmen's international passports differed were only 3 digits apart, that they held “Top Secret” and “do not provide information” markings and were issued by an authority normally reserved for intelligence officers and important officials.
It has now emerged that there are only 26 intervening passport numbers between Petrov's document and the cover passport for Col Shishmakov, who was organising the coup before the Montenegro's elections in October 2016 under the alias Eduard Shirokov.
The passport for Shirokov was issued in August 2016, suggesting that the special authority which issued it had only granted 26 passports from April 2016, when Petrov started travelling, to that point.
Interpol has issued wanted notices for Sismakov, under his alias Shirokov, after the plot to kill Milo Djukanovic, the prime minister at the time, was foiled only hours before it was due to be carried out