He and a colleague, Gerry Mahoney, had travelled to the city from Dublin via Milan on an Alitalia flight.

Their mission had already been rejected by a number of other firms for being "too risky". In a country where the shift towards capitalism has been marked by oligarchs (both in and out of favour with the government), an active mafia presence and arbitrary and illegal business takeovers, the two men were jumping into a nest of vipers.

Richter's firm, a branch of Belfast-based Priority Investigations, had been contracted to serve court papers on some of Russia's highest profile politicians and businessmen. All are board members of either the oil and gas giant Gazprom or state-owned Rosneft. It wouldn't be easy.

The two men even feared being shot as terrorists if they attempted to spring any surprises on their targets.

Among the people to whom they had to deliver legal documents were the Kremlin's deputy chief of staff, Igor Sechin, first deputy prime minister Dmitry Medvedev, the chief executive of Gazprom, Alexei Miller, and Rosneft vice-president Nikolai Borisenko. The documents named them as defendants in a case being taken by USbased shareholders in another Russian oil firm, Yukos.

The Irish investigators would make for unwelcome visitors as the Russian government prepares to float a $10bn stake in Rosneft, the world's second largest oil company, on the London and Moscow stock exchanges next month.

Twelve holders of US-listed Yukos stock, including the former US national security advisor Richard Allen, could put a spanner in the works. Rosneft took over the main production asset of Yukos in 2004 after a forced government auction, a move that tripled Rosneft's oil production.

The US shareholders claim that the planned flotation next month is an attempt to legitimise what they see as an illegal acquisition.

Yukos was born in the first years of the break-up of the Soviet Union. Its former chief executive, Mikhail Khodorkovsky, was arrested in 2003 . . . it is widely believed the establishment disliked his growing involvement in politics . . . while Yukos was hit by the government with a $7bn bill for alleged tax evasion.

Now the 12 US shareholders are seeking to recoup losses of $3.4m in a move that their lawyers claim could open up a flood of similar claims against Rosneft. One of its vicepresidents admitted last week that the litigation could depress the upcoming flotation.

But to even have a hope of getting their money, the shareholders needed Richter and Mahoney to deliver the documents to the named defendants. It was not certain that they would succeed.

Shortly after landing in Moscow, the two men were told their bags had gone missing en route from Milan. They had put all the documentation they needed to serve in their checked-in luggage.

They changed their accommodation plans at the last minute, booking in to an alternative one of the locations where they already had reservations.

After three days, their bags reappeared and they made their way to Sheremetyevo airport to collect them.

Richter said he and Mahoney were photographed by men in plain clothes.

Richter also claims they were followed by three men in a taxi as they returned to their city centre hotel. Two of the men, Richter said, seated themselves in the hotel reception area upon arrival.

That same day, Richter made his first attempt at serving the legal papers.

About 15km from Moscow city centre, the Rublyevo-Uspenskoye highway cuts through the preferred residential area for Russia's political elite and businessmen.

In Soviet days, it was home to the dachas of the privileged. President Putin and former president Boris Yeltsin live in the neighbourhood.

Today, the wealthy area split by the RublyevoUspenskoye highway draws outlets such as Italian car manufacturer Lamborghini, which chose the area to open its first ever Russian dealership last April.

Richter also knew that it was home to Gazprom chief executive Alexei Miller. As Richter's taxi progressed along the road, he noticed what seemed to be "many policemen" along the highway. The taxi was soon stopped and Richter was asked to produce his passport and visa.

"The police told me that my visa only gave me the right to travel in central Moscow and that I had no right to be in the area of the highway, " said Richter, who returned to his hotel.

That afternoon Richter and Mahoney attempted to serve documents on defendants at Gazprom, which leaves no room for doubt that uninvited guests are not welcome. Its headquarters at Nametkina Street, on a 1.5 squarekilometre compound, are patrolled by police and military, some with guard dogs, while its fencing has laser detection in case of attempted intrusion.

Gazprom was holding a press conference that day.

The two investigators attempted to mingle with journalists and photographers to gain entry to the headquarters.

They noticed they were being followed. After more than an hour the crowd was informed that the board of directors' meeting would not take place. It had been shifted to a Gazprom plant in Tomsk, in western Siberia, a three-hour flight from the capital.

The following day Richter and Mahoney returned to the Gazprom headquarters.

Richter told security guards he had a confidential delivery to make. When he told them and the receptionist the names of the intended recipients, the staff grew agitated and alarmed.

One security guard, said Richter, shouted at the two men that they would have to leave. Richter suggested that he sign for the documents. He refused, but in the end he agreed that Richter and Mahoney could leave them with security staff.

With that done, the two men left the compound and headed back to Dublin.

Back at home, an Alitalia representative informed them their luggage had been on the flight from Milan to Moscow and had not been missing. It seems mother Russia is still brimming with intrigue.

Richter may soon have to return to the Russian capital to undertake further work. The reception will certainly be cool. He and Mahoney may just have helped to cast a shadow over one of the country's biggest ever flotations.

CELTIC TIGER WEALTH BOOSTS PRIVATE INVESTIGATIONS

IAN WITHERS established Priority Investigations in 1960. In the course of his career he has worked with the British police and been a national security adviser to government of the Seychelles.

Now about to retire, he has seen signi"cant changes in the industry, and its clients, in the past few years, especially in Ireland. He said that increased wealth in the country has seen the level of business increase.

Much of the "rm's bread and butter business involves the tracing of debtors and family-related investigations concerning issues including "delity and runaways.

Assignments such as that in Moscow occur a few times a year, he said. The company carries out a risk assessment of such cases before accepting them. It recently turned down a job to serve court documents in Iraq, a proposition that was considered too risky.

The "rm has worked on behalf of company shareholders in the past, including those from Irish exploration and production "rm Bula Resources. Withers and his team helped o track down former chairman Jim Stanley after he moved to Moscow back in 1997.

Bula shareholders had paid stg£2.5m to an offshore company which, it transpired, was owned by Stanley, who had previously refused to divulge any interest in it. Some of the money was used to buy what turned out to be a useless Russian oil"eld.

Among Withers' other former clients are consumer champion Eddie Hobbs. He had been managing director of Taylor Integrated Planning Services. Its founder, Tony Taylor, absconded in 1996 after Hobbs discovered that more than 1.1m of investors' money had gone missing.

Hobbs paid Priority stg£25,000 to track down Taylor's exact address in England.

Taylor was later arrested, convicted of fraud, and served time in prison.