Investigators have determined that at least several of the suspicious packages that have been sent to locations across the U.S. this week were handled by a Florida U.S. Postal Service facility just north of Miami, a new report says.

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Investigators have nailed down that several of the packages were processed at a U.S. Postal Service facility in Opa-locka, Fla., according to CNN’s Evan Perez.

“This is one of several mail processing facilities in that area, that handles mail for the Miami area, the general South Florida region, and so the question is, you know, was the person who did this — were they in South Florida, did they come to South Florida to drop these off?” Perez said, during an interview with CNN’s Wolf Blitzer Thursday. “I think this is one of the first clues we're getting as they try to narrow down where this originated from, where the packages originated from. Postal service is going to be a key part of this investigation.”

Earlier Thursday, FBI Assistant Director William Sweeney refrained from sharing where the packages originated.

"Some were obviously in the postal system," Sweeney said during a press conference. "I'll leave it at that."

A series of suspicious packages were sent to figures including former President Barack Obama, former Secretary of State Hillary Clinton, and former CIA Director John Brennan.

The FBI said on Wednesday that additional packages may be issued to other locations, and that all of the packages had a return address of “DEBBIE WASSERMAN SHULTZ” [sic] in Florida. The packages are being analyzed at the FBI Laboratory in Virginia.