The investigative website Bellingcat has identified the second suspect responsible for poisoning Sergei Skripal as Alexander Mishkin, a doctor working for Russia’s GRU military spy agency.

The website said it had tracked down Mishkin’s real identity after obtaining a scanned copy of his actual passport. It had confirmed details with people who knew him and using open source information, it said.

Last month Bellingcat identified the other suspect, previously named as Ruslan Boshirov, as Col Anatoliy Chepiga, a special forces veteran.

Mishkin and Chepiga allegedly poisoned Skripal and his daughter Yulia in March using the Soviet nerve agent novichok. Both flew into the UK using the false identities of Boshirov and Alexander Petrov.

According to Bellingcat, Petrov is in fact Mishkin, a trained military doctor working undercover for the GRU. Mishkin’s passport, issued in 2001 in St Petersburg, gives his real name. He was born in Loyga, a village in the Archangelsk district of northern Russia, the document suggests.

Profile What is Russia's GRU intelligence agency? Show Powerful and mysterious, the GRU is one of Russia’s three intelligence agencies. It has been accused by the US of having taken the lead in hacking the 2016 US presidential election. Russia also has the FSB and SVR. The former is the sprawling structure that absorbed most parts of the KGB after the fall of the Soviet Union, while the latter is the part that focused on spying abroad, which became a new structure in modern Russia. The GRU, the intelligence wing of the Russian army, has always been a separate entity. All three run agents and missions abroad.

The GRU went into decline in the 1990s and there was some talk of disbanding it, but in 2006 it moved to new headquarters. It was considered instrumental in Russian manoeuvres to annex Crimea in 2014 and subsequent interference in eastern Ukraine.

The level of secrecy surrounding the GRU is so high that there was even speculation in 2016 that it had changed its name without anybody knowing.

Mishkin studied and graduated from one of Russia’s elite military medical academies, and was trained as a military doctor for the Russian naval armed forces.

During his studies, Mishkin was recruited by the GRU, Bellingcat said, and by 2010 he had relocated to Moscow. It was there he received his undercover identity – including a second national ID and a travel passport – under the Petrov alias.

The website is due to release further details at a press conference on Tuesday in the House of Commons. It will also publish a full report detailing how Mishkin was identified, along with witness interviews at 1pm.

It has established that Mishkin travelled extensively from 2011 to 2018 using his fake identity.

He made multiple trips to Ukraine and to the neighbouring breakaway Moscow-supported republic of Transnistria. His last trip to Kiev happened in December 2013, at a time when anti-government protests were taking place against Ukraine’s president Viktor Yanukovych. Yanukovych fled weeks later to Russia.

Chepiga was also involved in events in Ukraine, and received a state award for his “peace-keeping” role there. Unlike Chepiga’s cover identity, Mishkin’s includes authentic details from his own biography. His birth date, first and patronymic name – Yevgeneyvich – and the first names of his parents are the same.

The revelation is another astonishing development in the Skripal story. The government has identified both men as GRU officers and has accused Moscow of staging an attempted murder on British territory.

The Kremlin has vehemently denied this. But Chepiga and Mishkin’s appearance – under their cover names – on state TV prompted widespread mockery both at home and abroad.

The pair said they travelled from Russia to Skripal’s home city of Salisbury because they were attracted by its beautiful cathedral spire. They said they were forced to visit on two consecutive days because of heavy slush during their first trip.

Mishkin’s professional expertise as a medical specialist raises further questions. The poison novichok is one of the most dangerous nerve agents to have been manufactured in a laboratory. Three months after the unsuccessful murder plot, the British woman Dawn Sturgess died after unwittingly spraying novichok on her wrists.

Until early September 2014, Mishkin was registered as living at Khoroshevskoe Shosse 76B in Moscow: the address of the headquarters of the GRU. In the autumn of 2014, both Mishkin and Anatoliy Chepiga shifted to upscale apartments, Bellingcat reported.

Mishkin’s current military rank is unknown. The website said that based on the rank when he graduated – senior lieutenant – it was probably that he was either a Lt Col or a full colonel at the time of Skripal’s poisoning.

Bellingcat said that the evidence it would present on Tuesday includes interviews with people who knew Mishkin, both in St Petersburg and his home village of Loyga. It said it would also provide visual evidence confirming that Mishkin and “Petrov” were the same person.