(AP) A 69-year-old man was charged Friday with trying to extort $10,000 from the FBI in exchange for averting what a federal prosecutor called an “imaginary plot” to contaminate public water supplies in four Kansas and Missouri cities.

Manuel Garcia, of Kansas City, Mo., was charged in a criminal complaint and placed in federal custody pending a detention hearing, U.S. Attorney Tammy Dickinson said.

“There is no evidence that anyone actually possessed any chemicals to contaminate public water supplies,” Dickinson said in a news release. “The chemicals were as fictional as the conspirators in this imaginary plot.”

Investigators said in an affidavit that Garcia spoke of the plot in calls this month to the FBI, the Kansas City Police Department and the Alcohol, Tobacco and Firearms Joint Support Operations Center in Washington, D.C.

Garcia told the federal agents that two of his acquaintances planned to put an unknown chemical into the four cities’ water supplies, according to the affidavit.

Garcia said the two had tested their plan on horses that suffered convulsions and died. Garcia stated that for $10,000 and a grant of immunity he would attempt to locate his acquaintances, investigators said.

The affidavit states that Garcia was contacted Wednesday after an FBI agent recognized his voice on three of the calls. He lives close to a cell tower identified as the vicinity from which one of the calls originated, investigators said.

Garcia did not have a lawyer Friday.

In 2010, Garcia was sentenced to 18 months in federal prison after pleading guilty to making a phone call threatening to bomb the U.S. courthouse in downtown Kansas City.

Prosecutors said he placed a mesh cloth cooler outside the courthouse with a note saying it contained explosives, although it contained only telephone books. He also was accused of calling 911 to say three more bombs were inside the courthouse the next day.