Investigators believe that some of the 10 pipe bomb packages mailed to critics of President Donald Trump over the past week could have passed through a U.S. Postal Service facility in South Florida.

The Miami-Dade Police Department said they are assisting federal agents at the U.S. mail sorting facility in Opa-locka, Florida. A senior official told NBC News that they are trying to determine if some of the packages went through the center, which is the largest mail procession facility in South Florida.

The packages, all of which contained pipe bombs, have been addressed to former Vice President Joe Biden; actor Robert De Niro; Rep. Maxine Waters, D-Calif.; former Attorney General Eric Holder; former CIA Director John Brennan; former President Barack Obama; and former Secretary of State Hillary Clinton.

Biden and Waters each received two packages. The package sent to Brennan was addressed to CNN's offices in New York and led to an hourslong evacuation of the building Wednesday.

Holder's package was mailed to the wrong address and wound up being sent back to the return address written on the envelope, belonging to Rep. Debbie Wasserman Schultz, D-Fla.

All of the packages listed Wasserman Schultz's as the return address — in Sunrise, Florida, less than 20 miles north of Opa-locka.

The U.S. Postal Service said the facility there processes mail sent to all parts of the country, but only handles packages.

At least some of the devices sent were flawed in varying ways and would not have exploded, investigators said Thursday. But there's no way to know whether the deficiencies were intentional or the result of faulty construction.