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The trial in Italy is centred on corruption allegations against manufacturer Finmeccanica. Its British unit, AgustaWestland, was contracted by India in 2010 to supply 12 helicopters for Rs 3,600 crore.
In January 2013, India cancelled the deal and the CBI was assigned to investigate whether kickbacks were paid to Indian officials, as alleged in Italian courts.
At the time of cancellation, three helicopters had already been delivered to India against a payment of nearly Rs 1,100 crore.
Among those being investigated by the CBI in India is former Air Force Chief SP Tyagi, who was allegedly given kickbacks through a maze of companies who dealt with his cousins. He has denied any wrongdoing.
The CBI says that the former Air Force chief was instrumental in influencing decisions that changed the tender terms to favour the specification of AgustaWestland's helicopters.
Air Chief Marshal SP Tyagi was head of the Air Force from 2004-2007; he has asked how he could have played a role in a deal completed after he left his post.
The CBI says that the tender was changed to accommodate AgustaWestland by, among other things, lowering required altitudes where the helicopters could operate to 15,000 feet from 18,000 feet.
The tender terms were also allegedly changed to introduce an engine failure flying test. This favoured AgustaWestland as its helicopters were the only ones in the tender operating with three engines.
The CBI's investigators have travelled to Italy to meet the Italian prosecutors who have handled the case against Finmeccanica executives.
In recent years, India has emerged as the world's largest weapons importer, but procurements are periodically held up by allegations of corruption.
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