THE assassination of Alexander Litvinenko may be linked to the death of an international lawyer who died when his helicopter crashed near Bournemouth Airport two years ago, claim sources close to the former agent.

The case of Mr Litvinenko, who died in London last week after being poisoned by radioactive material, has already spawned numerous conspiracy theories.

The 43-year-old had been a critic of Russia's hardline President Vladimir Putin and his killing has been described as "an organised operation" bearing all the hallmarks of a foreign intelligence agency.

Now friends of Mr Litvinenko say they believe there is a connection with the death of Dorset millionaire lawyer Stephen Curtis, who was working for one of Russia's leading businessman.

At the inquest into the deaths of Mr Curtis, 45, and his Bournemouth based pilot, Max Radford, the coroner said the story had "all the ingredients of an espionage thriller."

The pair died when the Agusta 109 helicopter they were travelling in crashed and exploded in a fireball in a field on approach to Hurn on March 3, 2004.

Mr Curtis, 45, who owned a castle on Portland, was chief executive of Menatep, a company owned by Russian oil giant Yukos.

And his position at Menatep placed him right at the centre of a power struggle between Mr Putin and the boss of Yukos, Mikhail Khodorkovsky.

Mr Curtis took the reins of the company when Mr Khodorkovsky was jailed for tax fraud, a charge his supporters believe was trumped up by the Russian authorities for political reasons.

The inquest heard from relatives of Mr Curtis that the lawyer had received death threats and Mr Radford's father Dennis said the possibility of sabotage should be considered.

But accident investigators said they found no evidence the helicopter had been deliberately brought down and said pilot error was to blame.

However, the conspiracy theories have refused to go away and at the weekend, one insider close to Litvinenko said: "The inquest recorded accidental death but two weeks before the tragedy, Stephen said that if something happened to him, it would not be an accident.

"He had told of threats and felt he was under surveillance. I'm told he also got hold of a hit list' like Litvinenko and passed it on to the authorities."

Mr Litvinenko was apparently also investigating the murder of Russian journalist Anna Politkovskaya, a critic of President Putin, who was shot dead in October.