(NEW YORK) -- Investigators racing to identify who sent 10 mail bombs to former President Barack Obama, former Vice President Joe Biden, former Secretary of State and presidential candidate Hillary Clinton other public figures are chasing promising leads pointing them to South Florida as the potential origin for some of the menacing parcels, sources told ABC News on Thursday.
Law enforcement agencies were deploying additional resources to South Florida in an all-out effort to find who mass mailed the bomb packages that authorities say are meant to maim and kill, the sources said.
"We are investigating all this with great precision. I can say with certainty that we will identify and arrest the person or people responsible for these acts," New York police Commissioner James O'Neill said at a news conference Thursday afternoon. "Law enforcement professionals do not care about the politics involved in these acts."
Bill Sweeney of the FBI's New York office said an army of agents is "fully engaged" in the probe.
"This is a nationwide investigation involving multiple jurisdictions coast to coast," Sweeney said.
Everyone who has been sent explosive devices so far is a prominent critic of President Donald Trump, and many of them have been publicly disparaged by the president either at campaign rallies or on Twitter. Investigators have not determined a motive for the mail bombs.
All of the devices, which are now being analyzed at the FBI lab in Quantico, Virginia, went through the U.S. postal service. They were all intercepted before they reached their intended targets, sources told ABC News on Thursday.
Former Vice President Joe Biden and actor Robert De Niro are the latest high-profile figures to be sent explosive devices this week in an apparent mail-bomb campaign that investigators suspect is meant to maim and kill.
Two of the menacing packages were sent to Biden and intercepted in Delaware in the latest of the series of 10 mail bombs that law enforcement is responding to with a domestic terrorism investigation, sources told ABC News.
Philip Bartlett, head of the New York office of the U.S. Postal Inspection Service, said postal police have been aggressively searching the mail system and have not found any new devices since early Thursday morning.
"In terms of tracking, we have over 600,000 postal employees out there right now. We have the eyes and ears looking for these packages," Bartlett said. "I will say in the postal network, we have found nothing in the last eight hours. So what we have so far is what we have, 10 parcels."
Some critics of Trump said he has demonized all of those who have been sent the suspicious parcels, and claim his rhetoric may have inspired the mystery bomb maker or makers.
White House press secretary Sarah Sanders bristled at such a suggestion. "The president is certainly not responsible for sending suspicious packages to someone, no more than Bernie Sanders was responsible for a supporter of his shooting up a Republican baseball field practice last year," she said, referring to a shooting in June that seriously wounded House Majority Whip Steve Scalise, R-Louisiana.
"The idea that this is at the hands of the president is absolutely ridiculous," the press secretary said.
Trump, meanwhile, has said his administration is "extremely angry" about the mail bombs, but he is blaming the media.
"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 Thursday morning. "It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!"
Former CIA Director John Brennan, whose name was on a packaged mail bomb sent to CNN, responded to Trump’s media criticism, telling the president to "stop blaming others" and "look in the mirror."
"Your inflammatory rhetoric, insults, lies, & encouragement of physical violence are disgraceful. Clean up your act....try to act Presidential. The American people deserve much better. BTW, your critics will not be intimidated into silence," Brennan tweeted.
A search for where the bomb components were purchased
The FBI, Secret Service and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) were fanning out across the country to determine where components of the devices were purchased, which may give clues to who is responsible.
X-ray photographs of the devices exclusively obtained by ABC News illustrate the critical leads investigators are now pursuing: Each device contained a digital clock, explosive powder, a battery power source and wiring to channel a spark for detonation, sources told ABC News. The devices also included glass as potential shrapnel. None of the devices exploded, but they had the potential to maim or kill.
"The FBI advises the public to remain vigilant and not touch, move or handle any suspicious or unknown packages," the FBI said in a statement Wednesday evening. "We ask anyone who may have information to contact the FBI."
It's not entirely clear whether all of the incidents are linked, but authorities said they fear other bombs may have been sent.
Former President Jimmy Carter has been warned to be on alert for suspicious packages being sent to him, his spokeswoman told ABC News.
The various bubble-wrapped-lined manila envelopes with computer-printed labels and Forever stamps have been sent to the FBI's lab in Quantico, Virginia, for further analysis. The devices found inside are also being examined for fingerprints and DNA.
It began with a pipe bomb to George Soros
The series of mailed explosives began Monday with the discovery of a pipe bomb in the home mailbox of billionaire philanthropist George Soros in Westchester County, New York. Soros is a Democratic supporter often criticized by right-wing groups.
The following day, a package addressed to Hillary Clinton containing an explosive device was intercepted by the Secret Service at a screening facility before it reached her home in the New York City suburb of Chappaqua, also in Westchester County. Former President Bill Clinton was home at the time the package was found.
Hillary Clinton, speaking at a campaign event Wednesday in Florida, said, "We are fine, thanks to the men and women of the Secret Service who intercepted the package addressed to us long before it reached our home."
"But it is a troubling time, isn't it?" she added. "And it's a time of deep divisions and we have to do everything we can to bring our country together."
A package addressed to Obama containing an explosive device was intercepted by the Secret Service early Wednesday morning before it reached his residence in Washington, D.C.
Later that morning, a package containing an explosive and suspicious powder was found in the mail room of the Time Warner Center in Manhattan, which is home to CNN’s New York headquarters. It was addressed to former CIA director John Brennan, though he is an NBC News contributor and has no public ties to CNN.
The package addressed to Brennan traveled through the U.S. mail system, two officials briefed on the investigation told ABC News. It arrived at the Radio City post office in midtown Manhattan where it was picked up per normal procedure by a private courier who delivers the mail to the CNN office and other locations, the officials said.
The courier then hand-delivered all of CNN’s mail for that day, including the manila envelope with U.S. Postal Service first-class mail "forever" stamps, which feature the American flag. That’s how the package wound up in CNN’s screening and sorting mail room, the officials said.
There didn't appear to be any postal markings above of the stamps, which investigators are looking into.
Eric Holder, Maxine Waters among the targets
A mail-bomb was sent to former Attorney General Eric Holder with a return address for Democratic Rep. Debbie Wasserman Schultz in Florida. The package did not reach its intended destination and so it was sent to the congresswoman's address on Wednesday. Authorities do not believe Wasserman Schultz, former head of the Democratic National Committee, was involved in sending any of the packages.
Another package containing a device addressed to Democratic Rep. Maxine Waters of California was found in Los Angeles on Wednesday night. A prior one addressed to Waters was intercepted earlier Wednesday by Capitol Police in Washington, D.C.
The two packages sent to Biden, which were intercepted at different postal facilities in Delaware, and the one to De Niro brought the total under investigation into double digits Thursday morning.
The package addressed to De Niro was discovered at the actor’s Tribeca Productions film and television company in New York City early Thursday morning. A retired NYPD anti-terrorism detective who screens the mail for De Niro saw a photo of another suspicious package on the news and realized it was similar to one sent to the actor's production office on Tuesday, O'Neill said.
The mail bomb was removed by police in a bomb-containment vehicle.
Bryan Paarmann, special agent in charge of the FBI's Counterterrorism Division and Joint Terrorism Task Force in New York City, said at a press conference Wednesday that the mailings appear to be political in nature.
"The utilization of violence in order to further one's own political agenda is unacceptable to us," Paarmann told reporters. "We will turn over every rock, we will turn every corner and we will talk to everybody that we have to in order to mitigate this threat."
On Wednesday, from the White House, Trump said his administration is "extremely angry" about the incidents, adding that "the full weight of our government is being deployed to conduct this investigation and bring those responsible for these despicable acts to justice."
Democratic leaders noted that most of the people targeted had been ridiculed by Trump.
"We listened with great interest to the president's remarks this afternoon," the Democratic House and Senate leaders, Rep. Nancy Pelosi and Sen. Chuck Schumer, said in a joint statement Wednesday. "However, President Trump's words ring hollow until he reverses his statements that condone acts of violence."
"Time and time again, the president has condoned physical violence and divided Americans with his words and his actions: expressing support for the Congressman who body-slammed a reporter, the neo-Nazis who killed a young woman in Charlottesville, his supporters at rallies who get violent with protesters, dictators around the world who murder their own citizens, and referring to the free press as the enemy of the people," the Democratic leaders wrote.
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