Federal authorities arrested a man in Florida on on October 26 in connection with the mail-bomb scare that widened to 12 suspicious packages, the Justice Department said.
Law enforcement officers were seen on television examining a white van, its windows covered with an assortment of stickers, in the city of Plantation. They covered the vehicle with a blue tarp.
The man was in his 50s, a law enforcement official said, but his name and any charges he might face were not immediately known.
Department spokeswoman Sarah Isgur Flores said authorities planned to announce more information at a press conference.
Earlier on October 26, authorities said suspicious packages addressed to New Jersey Senator Cory Booker and former National Intelligence Director James Clapper both similar to those containing pipe bombs sent to other prominent critics of President Donald Trump had been intercepted.
The discoveries making 12 so far further spurred a coast-to-coast investigation, as officials scrambled to locate a culprit and possible motive amid questions about whether new packages were being sent or simply surfacing after a period in mail system.
The devices have targeted well-known Democrats including former President Barack Obama, former Vice-President Joe Biden, Hillary Clinton and former Attorney-General Eric Holder.
The FBI said the package to Mr. Booker was intercepted in Florida. The one discovered at a Manhattan postal facility was addressed to Mr. Clapper at CNN’s address. An earlier package had been sent to former Obama CIA Director John Brennan via CNN in New York.
Attorney-General Jeff Sessions said on October 26 the Justice Department was dedicating every available resource to the investigation “and I can tell you this - We will find the person or persons responsible. We will bring them to justice.”
Mr. Trump, on the other hand, complained that “this ‘bomb’ stuff” was taking attention away from the upcoming election and said critics were wrongly blaming him and his heated rhetoric.
Investigators were analysing the innards of the crude devices to reveal whether they were intended to detonate or simply sow fear just before Election Day.
Law enforcement officials told The Associated Press that the devices, containing timers and batteries, were not rigged to explode upon opening. But they were uncertain whether the devices were poorly designed or never intended to cause physical harm.
The package addressed to Mr. Booker was found during an oversight search of that facility, according to a law enforcement official.
The officials spoke on condition of anonymity because they were not authorised to discuss the ongoing investigation by name.