US officials said that on 24 May 2011, Mr Arbabsiar made contact with an informant for the US Drug Enforcement Agency, who was posing as a Mexican drug cartel member.
Over a series of meetings, it is said that details emerged of a conspiracy involving members of the Iranian government paying $1.5m (£960,000) for the assassination of Saudi ambassador Adel al-Jubeir on US soil.
But in conversations secretly recorded for the US authorities, Mr Arbabsiar also allegedly considered having the ambassador killed at a purported favourite restaurant, despite the possibility of mass casualties.
The plot would have been carried out with explosives, Mr Holder said. But he added that no explosives were ever put in place and the public was not in danger.
Mr Holder said Mr Arbabsiar, with approval from Mr Shakuri, wired $100,000 to a US bank account for the informant as a downpayment.
- They use a dual US-Iranian citizen. Probably the most monitored category of individual possible.
- Their agent contacts the Mexican drug cartels not in Mexico, but in the USA, probably to make conversation recording easier.
- They wire the downpayment to a US bank, not to Mexico or some offshore account.