Federal investigators said they had them under surveillance for at least seven months, infiltrating their meetings at a Waffle House, homes and other places, before finally arresting them Tuesday, just days after discovering evidence they were trying to extract ricin from castor beans.

“While many are focused on the threat posed by international violent extremists, this case demonstrates that we must also remain vigilant in protecting our country from citizens within our own borders who threaten our safety and security,” said U.S. Attorney Sally Quillian Yates.

The four gray-haired men — Frederick Thomas, 73; Dan Roberts, 67; Ray Adams, 65; and Samuel Crump, 68 — appeared in federal court Wednesday without entering a plea and were jailed for a bail hearing next week. They apparently had trouble hearing the judge, some of them cupping their ears.

Thomas and Roberts were charged with conspiring to buy an explosive device and an illegal silencer. Prosecutors would not say whether the men actually obtained the items. Adams and Crump were charged with conspiring to make a biological toxin.

Relatives of two of the men said the charges were baseless. The public defender assigned to the case had no comment.

Prosecutors said that Thomas was the ringleader and that he talked of carrying out the sort of actions described in “Absolved,” an online novel written by former Alabama militia leader Mike Vanderboegh. In the book, the militia members build rifle grenades and drop explosives from crop dusters.

In the book’s introduction, Vanderboegh calls it a “cautionary tale for the out-of-control gun cops of the ATF.”

“For that warning to be credible, I must also present what amounts to a combination field manual, technical manual and call to arms for my beloved gunnies of the armed citizenry,” he writes. “They need to know how powerful they could truly be if they were pushed into a corner.”

In an interview, Vanderboegh said he didn’t know the four men and bears no responsibility for the alleged plot.

“I’m glad that the FBI has apparently short-circuited some weak-minded individuals from misinterpreting my novel,” he said.

Last year, Vanderboegh was denounced for calling on citizens to throw bricks through the windows of local Democratic headquarters across the country to protest President Barack Obama’s health care plan. Several such incidents occurred. Vanderboegh has also appeared as a commentator on Fox News Channel.

Vanderboegh wrote on his blog Wednesday that his book was fiction and that he was skeptical a “pretty geriatric” militia could carry out the attacks the men were accused of planning.

But Kent Alexander, a former U.S. attorney in Atlanta, said he wouldn’t write off the men as harmless just because of their age: “Crime doesn’t have a retirement age. These guys are older than one usually sees, but criminals come in all ages.”

Donnie Dixon, another former U.S. attorney, said: “I would find it extremely difficult to think they could carry out a plot of such grandiose design, which doesn’t mean they should not have been nipped in the bud just like they were.” He said it would not have required anything grandiose “to cause a lot of problems or hurt a lot of people.”

Thomas’ wife, Charlotte, told The Associated Press the charges were “baloney.”

“He spent 30 years in the U.S. Navy. He would not do anything against his country,” she said. “He loves his country.”

Roberts’ wife, Margaret, said her husband retired from the sign business and lives on a pension. “He’s never been in trouble with the law. He’s not anti-government,” she said. “He would never hurt anybody.”

Ricin is a castor-bean extract whose potential as a deadly biological weapon has long been known. In 1978, Bulgarian defector Georgi Markov was assassinated in London with a ricin pellet believed to have been fired from the tip of an umbrella.