Federal agents searched a U.S. mail facility near Miami on Thursday night in the race to find who sent 10 pipe bombs to prominent Democrats and critics of U.S. President Donald Trump as leads pointed to Florida as the packages’ possible origin.
Investigators treated the devices as “live” explosives, not a hoax, said James O’Neill, the police commissioner of New York City, where two of the packages have turned up since Wednesday.
A federal law enforcement source told Reuters the devices were thought to have been fashioned from bomb-making designs widely available on the internet.
Investigators believe the packages, which were intercepted before reaching their intended recipients, went through the U.S. Postal Service at some point, that source said. None detonated and no one has been hurt.
WATCH: Manhunt intensifies after more pipe bombs sent to Trump critics.
Homeland Security Secretary Kirstjen Nielsen, in an interview with Fox News Channel, confirmed that at least some of the packages were mailed in Florida.
“Some of the packages went through the mail. They originated, some of them, from Florida,” she said. “I am confident that this person or people will be brought to justice.”
A bomb squad examined a mail distribution center near Miami where authorities believe several of the packages were processed, Miami police said.
Miami-Dade County Police said their bomb squad and its canine unit were on the scene in Opa-locka, Fla., as a precautionary measure, working alongside federal authorities.
Authorities have branded the parcel bombs, coming less than two weeks before national elections, as an act of terrorism, though they have declined to say how functional the devices were.
A number of bomb experts and security analysts said that based on the rudimentary construction of the bombs, it appeared they were more likely designed to sow fear than to kill.
WATCH: Joe Biden says ‘we’ve got to turn off this hate machine’ in reaction to pipe bombs
The first package surfaced on Monday at the Westchester County, N.Y., home of billionaire financier George Soros, a leading donor to the Democratic party and various liberal causes.
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On Wednesday, the FBI identified five more targets — former president Barack Obama, former secretary of state Hillary Clinton, former attorney general Eric Holder, former CIA director John Brennan and California Rep. Maxine Waters. Two packages were found addressed to her.
Brennan’s package was sent in care of the Manhattan bureau of CNN, where he has appeared as an on-air analyst.
Target list expands
On Thursday, the investigation widened with the discovery of three additional packages — two intended for former vice-president Joe Biden in his home state of Delaware and one for Hollywood actor Robert De Niro in Manhattan.
“It does remain possible that further packages have been or could be mailed,” William Sweeney, assistant director of the Federal Bureau of Investigation, told an afternoon news conference in New York.
The FBI has said at least five of the packages bore a return address for the Florida office of Rep. Debbie Wasserman Schultz, who formerly chaired the Democratic National Committee. Holder’s package ended up rerouted and delivered to the Wasserman Schultz return address.
Sweeney said the manhunt for perpetrators involved hundreds of investigators nationwide.
WATCH: Pipe bomb saga fuels political divisions in the U.S.
The bombs have heightened what already was a contentious campaign season ahead of the Nov. 6 elections, in which Trump’s Republican Party will try to maintain majorities in the Senate and House of Representatives. Democrats have seized on the episode as a symptom of the harsh rhetoric Trump wields against his rivals.
Trump condemned the bombs but later blamed the media, his frequent foil, for much of the angry tone in the nation’s political discourse.
No one has claimed responsibility, and the public was asked to report any tips. The parcels each consisted of a manila envelope with a bubble wrap interior containing “potentially destructive devices,” the FBI said. Each bore a computer-printed address label and six “forever” postage stamps, the agency said.
Some of the packages sent to New York locations had envelopes of white powder in them, but Sweeney’s examination had shown the substance posed no biological threat.
Sweeney said all of the devices were being sent to the FBI’s crime lab in Quantico, Va., for analysis.
Most of the intended recipients were high-profile Democrats, and all were known to be outspoken critics of Trump, foils for his political rhetoric or both.
WATCH: Bomb expert says pipe bombs sent to various Democrats can yield ‘tremendous amount’ of evidence
Trump long questioned Obama’s U.S. citizenship and referred to Clinton, whom he defeated in the 2016 presidential race, as “crooked Hillary.” He has derided Waters publicly as “low-IQ Maxine.”
The president revoked Brennan’s security clearance after the ex-CIA chief, a veteran intelligence official in Democratic and Republican administrations, lambasted Trump’s Russia summit performance as “nothing short of treasonous.”
Biden once said he would have fought Trump if they were in high school, while De Niro received a loud ovation when he hurled an obscenity at Trump at the Tony Awards in June.
At a Wisconsin rally on Wednesday night, Trump, who has denounced news media organizations as an “enemy of the people,” called attention to “how nice I’m behaving tonight,” but on Thursday morning he attacked the media again.
“A very big part of the Anger we see today in our society is caused by the purposely false and inaccurate reporting of the Mainstream Media that I refer to as Fake News,” Trump tweeted. “It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!”
WATCH: Robert De Niro, Joe Biden among prominent Democrats sent pipe bombs