Nigeria's secret service said on Wednesday that a British and Italian hostage killed by their captors last week were executed before a failed raid to free them had even taken place, and that the kidnap gang leader had died in custody.

Chris McManus and Franco Lamolinara were killed by their captors on March 8 before Nigerian and British special forces could free them during a raid on the house where they were being held. They had been kidnapped last May while working for a construction company in northwest Nigeria.

An earlier version of their murders, based upon an account from the wife of one of the kidnappers, suggested that the duo was killed during a failed rescue attempt.

But Doyin Adetuberu, a State Security Services (SSS) spokesman, said on Wednesday they had been killed before the raid had even begun.

He made the declaration as he paraded six of the kidnap suspects in front of the media in Abuja. He said they were all members of Islamist sect Boko Haram and had been arrested in a raid on March 7.

Apparently acting on the directive of the member of the sect who escaped from Zaria, the guards murdered the hostages before the arrival of security forces.

He said the kidnap gang's alleged ringleader, a man going by the name of Abu Mohammed, had been taken alive in the March 7 raid, but had died in custody two days later of gunshot wounds inflicted during his capture. It was that initial raid which led the authorities to the house where the hostages were being kept.

Investigations revealed that the plot was masterminded by the Abu Mohammed-led faction of Boko Haram. Following a raid ... on his hideout on March 7, Abu Mohammed and five others were arrested, Adetuberu told reporters.

DIFFERENT VERSIONS

The statement that the hostages were dead before the rescuers even arrived contradicts testimony from the wife of one of the guards, who told Reuters the two men were taken into a toilet and shot dead during the abortive rescue attempt.

The floor of the toilet where she said the hostages had been shot was coated in semi-dried blood. The sink had been ripped off and lay next to a plastic waste paper basket and a bottle of bleach on Saturday.

Upon the arrival of security forces at the building where the hostages were being held, there was a prolonged exchange of gunfire during which three of the guards were killed, said Adetuberu.

Three youths who conducted surveillance on McManus and Lamolinara before their abduction had also been arrested, he added.

The raid caused a diplomatic row between London and Rome over Britain and Nigeria's failure to inform the Italian government before launching the botched rescue mission.

Prime Minister Mario Monti called Nigerian President Jonathan and asked for a complete reconstruction of the operation as soon as possible.

Abu Mohammed's death in police custody is likely to raise eyebrows among Nigeria's angry Islamists.

Boko Haram's founder Mohammed Yusuf died in police custody following an uprising which killed hundreds in 2009. The sect, which carries out almost daily attacks in the northeast, still cites this as one of the reasons it targets the police.

A short video that emerged in August showed the hostages in captivity. They said they were being held by al Qaeda, although this could not be independently verified at the time. The video showed the two men blindfolded and on their knees, while three armed men stood behind them, their faces hidden.

A purported Boko Haram spokesman on Friday denied any part in their kidnapping.

Security officials say Boko Haram has received some training, weapons and bomb-making technology from al Qaeda in the Islamic Magreb, which operates in neighbouring Niger and Chad. The militant group is fighting to impose Islamic Sharia law in a country split between Christians and Muslims.

(Writing by Joe Brock; Editing by Tim Cocks and Andrew Osborn)