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ST. LOUIS – Authorities busted a ring of dangerous armed robbery suspects that investigators say targeted and terrorized more than 20 businesses in three months. Now the suspects could be behind bars for years, especially since the case is in federal court.

Four of the six suspects were in court at the Eagleton building this morning for arraignments.

The lead prosecutor, Assistant U.S. Attorney Paul D’Agrosa, says cooperation between law enforcement agencies helped to crack this case.

“It’s a scary situation to be robbed at gunpoint,” says DeMonte Benjamin, who manages a Metro PCS cellphone store on Goodfellow just north of I-70 in north St. Louis.

Surveillance video shows a frightening incident at his store back on September 22.

A man came in with a gun in his right hand and demanded cash, throwing a bag at DeMonte. There were two customers in the store at the time.

DeMonte complied and the man left with cash and cellphones.

“He knew what he was doing. He was very smooth, you know? He was very bold; there was a couple of customers in there, there’s only one of him so he knew what he was doing,” DeMonte said.

That was one of the bold and brazen robberies that a ring of six people were charged with in federal court.

Investigators say the group hit some 21 businesses between July and the end of September, most of them in the City of St. Louis.

An 18-count federal indictment details what authorities call a conspiracy by the suspects to commit armed robberies and disrupt interstate commerce.

Assistant U.S. Attorney Paul D’Agrosa says the suspects used three weapons including a distinctive purple and black handgun.

“The purple gun was used in a lot of the robberies, a Draco which is like an AK-47 style handgun was used and another black handgun,” said D’Agrosa.

Besides Metro PCS, other targets included Dominos, Papa John’s, Subway, O’Reilly Auto Parts, and Mr. Nice Guy.

Five of the six suspects are in custody, but Darnell Duncan is still on the loose.

D’Agrosa says the suspects had a similar motive in their robberies and that helped to tip off authorities.

“They would come into the store, one sometimes two, always armed. They would demand the safe, even if there was time delay on the safe the robbers would wait in the store until the delay finished and then they would take the money out of the safe,” said D’Agrosa.

Fortunately, nobody was hurt in the crimes.

DeMonte is grateful that people have been arrested.

And D’Agrosa says the federal charges could bring very stiff sentences.

“It does put ease to my mind and I’m sure the other customers or whoever got robbed in their past that, you know, they’re grateful that he’s behind bars and they’re going to serve X amount of time for whatever they did,” said DeMonte.

D’Agrosa added, “We will catch you and you will be punished, and you will be punished severely.”

D’Agrosa says there is a reward through Crimestoppers to get Duncan into custody.

Authorities want him off the streets so that all of the suspects can be behind bars.

Besides the US Attorney’s office, the St. Louis Metropolitan Police Department and the FBI also worked on the case.