WASHINGTON -- It was Saturday morning when Frank Janssen answered a knock at his door. He was zapped with a stun gun and kidnapped.

The 63-year-old Wake Forest, N.C., man was then stuffed in a car and driven 400 miles to Atlanta, where sources say he was held captive by people linked to the violent Bloods street gang.

Frank Janssen CBS News

On Monday, Janssen's wife began receiving threatening messages and a picture showing him tied up in a chair.

"We will send (Janssen) back to you in 6 boxes," one text read. "And every chance we get we will take someone in your family to Italy and torture them and kill them."

Sources say the kidnappers were working for Kelvin Melton, a gang leader serving a life sentence in a North Carolina prison. Melton was convicted in a case prosecuted by Janssen's daughter, Colleen, an assistant district attorney.

Court papers show the FBI traced the messages to phones belonging to Melton's crew and to a cellphone Melton was using inside the prison.

Kelvin Melton CBS News

At 8:20 p.m. Wednesday, the FBI listened in on a call as a man believed to be Melton gave orders to kill Janssen.

"Get a bag, put it over his head, stuff something in his mouth," the caller said. "Make sure to clean the area up. ... Don't leave any DNA behind."

About three-and-a-half hours later, the FBI's Hostage Rescue Team raided an apartment in Atlanta and found Janssen alive.

Five people -- two women and three men -- have been arrested and charged with kidnapping. Sources say the FBI is still looking for others who may have been part of the plot.