Investigators have been searching coast to coast for the culprit and motives behind the bizarre mail bomb plot aimed at critics of the president, analyzing the innards of the crude devices to reveal whether they were intended to detonate or simply sow fear two weeks before Election Day. Three more devices were linked to the plot Thursday — two addressed to former Vice President Joe Biden and one to actor Robert De Niro — bringing the total to 10 in an outbreak of politically loaded menace with little if any precedent. Authorities warned there might well be more. Law enforcement officials told The Associated Press that the devices, containing timers and batteries, were not rigged like booby-trapped package bombs that would explode upon opening. But they were uncertain whether the devices were poorly designed or never intended to cause physical harm. A search of a postal database suggested at least some may have been mailed from Florida, one official said. Investigators are homing in on a postal facility in Opa-locka, Florida, where they believe some of the packages originated, another official said.

A member of the New York Police Department bomb squad is pictured outside the Time Warner Center in the Manhattan borough of New York City after a suspicious package was found inside the CNN Headquarters in New York, U.S., October 24, 2018. Kevin Coombs | Reuters

The officials spoke on condition of anonymity because they were not authorized to discuss the ongoing investigation by name. Homeland Security Secretary Kirstjen Nielsen, in an interview Thursday night with Fox News Channel, acknowledged that some of packages originated in Florida. New details about the devices came as the four-day mail bomb scare spread nationwide, drawing investigators from dozens of federal, state and local agencies in the effort to identify one or more perpetrators. The targets have included former President Barack Obama, Hillary Clinton, CNN and Rep. Maxine Waters of California. The common thread among them was obvious: critical words for President Donald Trump and frequent, harsher criticism in return. Trump claimed on Friday he was being blamed for the mail bombs addressed to his critics, complaining in a tweet sent before dawn: "Funny how lowly rated CNN, and others, can criticize me at will, even blaming me for the current spate of Bombs and ridiculously comparing this to September 11th and the Oklahoma City bombing, yet when I criticize them they go wild and scream, 'it's just not Presidential!'" Donald Trump tweet At a press conference Thursday, officials in New York would not discuss possible motives or details on how the packages found their way into the U.S. postal system. Nor would they say why none of the packages had detonated, but they stressed they were still treating them as "live devices." "As far as a hoax device, we're not treating it that way," police Commissioner James O'Neill said. Details suggested a pattern — that the items were packaged in manila envelopes, addressed to prominent Trump critics and carried U.S. postage stamps. The devices were being examined by technicians at the FBI's forensic lab in Quantico, Virginia.

A package containing a "live explosive device" according to police, received at the Time Warner Center which houses the CNN New York bureau, in New York City, U.S. is shown in this handout picture provided October 24, 2018. CNN/Handout | Reuters