A 58-year-old naturalized U.S. citizen pleaded guilty on Wednesday to conspiring with Iranian military officials in a plot to kill the Saudi Arabian ambassador to the U.S. while in Washington, D.C., last year.

Federal officials have charged Manssor Arbabsiar with three counts of conspiring to commit an act of terrorism against the United States, using foreign commerce facilities while attempting to carry out a “murder for hire,” and conspiring to do so.

Arbabsiar told U.S. officials that — at the direction of Iranian-based military leaders — he traveled in 2011 to Mexico, where he attempted to hire a member of a drug cartel to kill the Saudi ambassador for $1.5 million. But the gun-for-hire was really a confidential informant for the Drug Enforcement Administration (DEA).

The murder was set to take place at a Washington restaurant that was also frequented by senators, and the conspirators allegedly were willing to kill as many bystanders as needed to get the job done, saying that it was no “big deal,” according to federal officials.