Before authorities seized a cache of machine guns, rocket launchers and pipe bombs from a Willmar man’s bunker earlier this year, prosecutors say he discussed targeting a judge and two attorneys with homemade bombs.

A federal grand jury indicted Chad Lee Monson last week on 18 counts, including numerous firearms violations, tied to an arsenal law enforcement officers found when they searched his rural Kandiyohi County property. But earlier allegations from county prosecutors hint at a deadly plot cut short.

Monson, who is also awaiting trial on state criminal charges, made a brief first appearance in federal court in St. Paul on Tuesday and will return Friday for a detention hearing and arraignment. His attorney, Daniel Mohs, declined to comment until after Friday’s hearing.

The new indictment concerns the alleged illegal possession of 10 machine guns — two of which had “obliterated” serial numbers — and unregistered pipe bombs and silencers. The indictment also marks the latest chapter in a dramatic case that began with a tip from an informant and featured violent threats allegedly made by Monson’s sister against a witness.

Monson, who once owned excavation and gravel crushing companies with his ex-wife, was among five people arrested during a Jan. 30 raid of his home by drug and gang task force agents.

Dennis Larson, of Montevideo, said he had loaned Monson numerous pieces of equipment to aid his struggling businesses in recent years. At one point, Larson said, Monson showed him one of his grenade launchers and led him on a tour of a well-stocked underground safe. But Larson said their relationship soured when he sought to repossess the loaned goods. In 2014, Monson was also charged with stealing a payloader in North Dakota. Before long, Larson said, Monson’s business ventures were mired in financial or other failures.

“He was just doing drugs and making bombs,” Larson said in an interview this week.

Cache of weapons

When police combed Monson’s property in January, they found drugs, weapons and ammunition in nearly every corner, the state criminal complaint said — plus a bus that had been converted into living quarters for one couple.

Monson kept meth, cocaine and marijuana inside a bedroom safe that also held a rifle and a handgun. Officers also found “miscellaneous books on incendiary devices,” drug test kits and a device that can be used to cheat urine tests. At the time of the search, Monson was on probation for a 2017 drug conviction.

One of two rocket-propelled grenade launchers officers found was on display in a basement living room, the complaint said. The basement also concealed a concrete “bunker” room that required entry through a hidden door. After Monson shared an entry code to the room, law enforcement officers found additional drug paraphernalia, 15 firearms, component parts for a Thompson submachine gun, Uzis and AK-47s, homemade silencers and more than 10,000 rounds of ammunition.

According to the state complaint, Monson admitted to using the drugs and owning the firearms found in his bedroom and bunker. Officers found more methamphetamine, drug paraphernalia and 18 firearms in another defendant’s bedroom, including a second grenade launcher.

The U.S. attorney’s office declined to comment on the case.

Monson’s alleged remarks to an unidentified person about locating the addresses of a judge, prosecutor and another attorney on whose property he planned to “use or plant” explosives will likely factor into whether a judge will order Monson to remain in jail until trial. The identities of Monson’s purported targets were not disclosed in the state criminal complaint, nor was the name of the person to whom he allegedly described those plans.

About a month after Monson’s arrest, his 32-year-old sister sent a threatening Facebook message to an unidentified male witness. Amy Lynn Monson, of Burnsville, has since been charged with first-degree tampering with a witness after writing, “I know what u did and u will pay for it. watch ur back.”

The man shared the message with authorities, who said Monson admitted sending the message.

“Monson went on to state that if [the witness] is making this report to law enforcement,” the complaint said, “he must be scared but that he should be ‘more afraid’ of Chad Monson than of her.”

Stephen Montemayor • 612-673-1755 Twitter: @smontemayor