The man accused of mailing more than a dozen pipe bombs to prominent Democrats, other high-profile liberal figures and CNN had been plotting the "domestic terrorist attack" for months, prosecutors said.
The FBI searched electronic devices belonging to the suspect, 56-year-old Cesar Sayoc, and discovered files containing the addresses of his intended victims, as well as return labels that match those used on the padded mailing envelopes carrying the improvised explosive devices (IEDs), according to a letter from prosecutors sent Tuesday to the judge presiding over Sayoc's case in Florida.
"The defendant conducted a domestic terrorist attack targeting at least 15 victims," Geoffrey S. Berman, the United States Attorney for the Southern District of New York, wrote in the letter to U.S. Magistrate Judge Edwin Torres of the Southern District of Florida. "Metadata from the electronic devices indicates that the defendant started planning the attack as early as July 2018."
A document created on Sayoc's laptop on July 26 contains repeated copies of the return address in Sunrise, Florida, that was used on the parcels as well as the name of Democratic Rep. Debbie Wasserman Schultz. Moreover, the internet search history on Sayoc's cellphone reveals he was looking for the home address of former Secretary of State Hillary Clinton as far back as July 15, according to the letter.
Other files from Sayoc's laptop also contained addresses for "numerous additional targets," and the FBI is warning each of those individuals, the letter states.
"The evidence of the defendant’s terror campaign is still being collected but is already overwhelming," Berman wrote. "Put simply, only the defendant's arrest and incapacitation resulting from his detention were sufficient to stop his attack."
Berman requested that the Florida resident be transferred to New York to "face the consequences of his actions" and urged that he remain behind bars pending trial "due to both his dangerousness to the community and risk of flight."
"There are no conditions that could adequately protect the public from the defendant and assure his appearance in Manhattan for trial," Berman wrote.
Sayoc was arrested Oct. 26 following a days-long, nationwide manhunt. Authorities apprehended him in the parking lot of an Auto Zone mechanic shop in Plantation, Florida.
Sayoc could be sentenced to up to 48 years in prison if convicted of the five federal charges he's facing: interstate transportation of an explosive, illegal mailing of explosives, threats against former presidents and certain other persons, threatening interstate communications, and assaulting current and former federal officers.
He appeared in federal court in Miami on Monday, for the first time since his arrest. He was flanked by his three newly retained private attorneys, Dan Aaronson, James Scott Benjamin and Peter Patanzo.
A pretrial detention hearing was set for Friday morning. Sayoc had not yet entered a plea.
His attorneys did not immediately respond to ABC News' request for comment Wednesday.
'We do believe we caught the right guy'
Investigators were able to compare a fingerprint from one of the envelopes sent to a Democratic congresswoman and compared it to a sample collected from one of Sayoc's previous arrests in Florida, according to FBI Director Christopher Wray.
Sayoc's DNA was also found on some of the wires used in the IEDs, according to law enforcement officials.
"We do believe that we caught the right guy," Wray said at a press conference Oct. 26.
One of Sayoc's attorneys told ABC News after Monday's court appearance that the fingerprint and DNA evidence is "in question" and requires a complete forensic analysis.
Sayoc was tracked down using a mobile phone, sources told ABC News. Authorities have recovered a cellphone, a laptop computer and other electronic devices from him.
Sayoc's residence is listed as his mother's home in Aventura, but he was, for a time, living in the white van covered in stickers of President Donald Trump, which is now being investigated.
Sayoc is expected to be prosecuted in federal court in New York City, a senior law enforcement official told ABC News last week.
Court documents reviewed by ABC News show that Sayoc has a long history of criminal charges, including at least eight arrests in Florida alone, ranging from giving false information to get a refund to grand theft auto.
In 2002, Sayoc was arrested for threatening to discharge a destructive device after he allegedly called Florida Power & Light and "threatened to blow up" the power utility company, allegedly saying "it would be worse than September 11," the arrest record states. He pleaded guilty and was ultimately sentenced to probation, according to court documents.
Court documents also show that, in 2014, Sayoc worked as a "road manager for a variety of traveling male revue shows."
At least 15 IEDs intercepted so far
So far, authorities have recovered at least 15 IEDs that Sayoc allegedly mailed throughout the country. Each device was packaged in a tan-colored manila envelope lined with bubble wrap and stamped with approximately six postage stamps bearing an image of an American flag, according to court documents.
All of the addressees are prominent critics of Trump, and many of them have been publicly disparaged by the president either at campaign rallies or on Twitter.
Each envelope listed Schultz as the return sender at a particular address in Sunrise, Florida. Authorities do not believe the congresswoman, who is the former head of the Democratic National Committee, was involved in sending any of the parcels.
All of the packages traveled through the U.S. Postal Service. They were all intercepted before they reached their intended targets, sources told ABC News.
None of the devices detonated, and no one was injured in handling the packages.
"These are not hoax devices," Wray said at the Oct. 26 press conference.
The packages and the contents were all sent for analysis to FBI's laboratory in Quantico, Virginia.
"The FBI's analysis of the defendant's IEDs is ongoing, but it is clear that they were dangerous," David Brown, FBI special agent, wrote in the Oct. 26 complaint against Sayoc. "The IEDs that have been analyzed thus far contained energetic material with explosive qualities. The defendant also placed shards of glass in several of the IEDs for the apparent purpose of maximizing harm to his intended victims through the detonation of the devices that he had mailed."
Investigators have not determined a motive for the suspected mail bombs.
George Soros, Hillary Clinton, Barack Obama, CNN among the targets
The series of mailed explosives first came to light on Oct. 22 with the discovery of a package containing an IED that was delivered to the home of billionaire philanthropist George Soros in Westchester County, New York.
Inside the parcel was also a photograph of Soros marked with a red "X," according to court documents.
Soros is a Democratic supporter often criticized by right-wing groups.
The following day, a package addressed to Hillary Clinton containing an IED 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 in Florida on Oct. 24, 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 former President Barack Obama containing an IED was intercepted by the Secret Service early Wednesday morning before it reached his residence in Washington, D.C. Inside was also a photograph of Obama marked with a red "X," according to court documents.
Later that morning, a package containing a IED was delivered to CNN's New York headquarters the Time Warner Center in Manhattan. It was addressed to former CIA Director John Brennan, though he is an NBC News contributor and has no public ties to CNN.
Inside the parcel was also a photograph of Brennan marked with a red "X," according to court documents.
A package containing an IED was sent to former Attorney General Eric Holder with a return address for Wasserman Schultz. The parcel did not reach its intended destination and so it was sent to the congresswoman's address on Oct. 24. Investigators do not believe Wasserman Schultz was involved in sending any of the parcels.
Two packages, each containing an IED, were sent to Democratic Rep. Maxine Waters of California at her offices in Los Angeles and Washington, D.C. At least one of the parcels discovered on Oct. 24 included a photograph of Waters marked with a red "X," according to court documents.
Two packages, each containing an IED, were sent to former Vice President Joe Biden at separate addresses in Delaware but were unsuccessfully delivered on Oct. 25
A package containing an IED addressed to Robert De Niro was recovered from the actor’s Tribeca Productions film and television company on Oct. 25.
A package containing an IED addressed to Democratic Sen. Cory Booker of New Jersey was recovered in the United States Postal Service's Royal Palm Mail Processing Center in Opa-locka, Florida, on Oct. 26.
A package containing an IED addressed to former Director of National Intelligence James Clapper was then discovered at a United States Postal Service office in New York City.
A package containing an IED addressed to Democratic Sen. Kamala Harris of California was recovered from a post office in Sacramento, California, on Oct. 26.
Shortly after Sayoc was arrested on Oct. 26, authorities intercepted another explosive-laden package that was sent to Tom Steyer in San Francisco. Steyer is a billionaire philanthropist and top donor to Democrats.
On Monday, the day of Sayoc's initial court appearance, authorities recovered a fifteenth IED before it reached its intended target at CNN's office in Atlanta.
Trump points blame at media
Speaking from the White House on Oct. 26, Trump said the suspect will be prosecuted "to the fullest extent of the law."
"These terrorizing acts are despicable and have no place in our country," the president said. "We must never allow political violence to take root in America."
But that evening, from a rally in Charlotte, North Carolina, Trump appeared once again to cast blame on the media for the bomb scare.
"The media has a major role to play, whether they want to or not," he said.
ABC News' Mark Crudele, Jack Date, Katherine Faulders, Armando Garcia, Aaron Katersky, Mike Levine, Josh Margolin and Pierre Thomas contributed to this report.