The US accuses the Quds Force (QF), the external operations wing of Iran's Revolutionary Guard, of being behind the plot. Given the hierarchy of the Iranian regime, such a huge undertaking would have required a direct order from the supreme leader, Ayatollah Ali Khamenei, who personally controls the QF.
Khamenei's involvement would be surprising, to say the least. Throughout his tenure – since the death of the Islamic republic's founder, Ayatollah Ruhollah Khomenei in 1989 – he has shown himself to be highly cautious and devoted to entrenching the power of the clerical regime.
Another possibility is that Ayatollah Khamenei crafted the plot to provoke an attack on Iran by a foreign country, allowing him to shore up domestic support – but threats to his power are few right now, according to the Guardian. And it doesn't even make sense for QF to be behind it either, the Guardian piece argues; the plot was simply too sloppy for the group. Or perhaps it is a rogue operation, and that's why it wasn't as water-tight an operation as normally seen from the QF, which wouldn't be caught transferring money for the plot into US accounts, for instance.