He told U.S. District Judge Jed S. Rakoff that he did not intend for the devices to explode but was aware of the risk that they might.
While none of the devices detonated, Wray said they were "not hoax devices".
In addition to 16 counts of the use of weapons of mass destruction, Sayoc pleaded guilty to the interstate transport of explosives, the illegal mailing of explosives with the intent to kill or injure and the carrying of explosives during the commission of a felony, among other crimes. In exchange for his guilty plea, prosecutors dropped a charge that carried a mandatory life sentence. Each of the latter counts could mean 20 years in prison.
William F. Sweeney Jr., assistant director in charge of the FBI's NY office, said in a statement in November that "Cesar Sayoc deliberately targeted 13 individuals with 16 improvised explosive devices, attempting to create an atmosphere of fear and intimidation from California to the eastern seaboard".
The bombs began turning up weeks before the hotly contested midterm elections, contributing to an already tense political environment.
Authorities arrested the suspect in October at an auto parts store in Plantation, Florida, located about 20 miles from Opa-locka, where investigators discovered several suspicious packages in a us postal facility.
Sayoc was arrested last October in Florida outside a van he was living that was covered in a variety of right-wing political bumper stickers, including one with rifle scope images over the faces of Hillary Clinton and former President Barack Obama, as well as a massive portrait of Trump.
Authorities said all 16 were similar, describing them as "improvised explosive devices" containing pipe filled with explosive material, wiring and a small clock.
"Did you intend they would explode?" the United States district judge Jed Rakoff asked. At times he seemed confused and asked the judge questions.
"What would prevent powder from fireworks from exploding?"
"I am extremely sorry", he said in a voice barely above a whisper.
A device addressed to the Clintons was discovered the following day, followed a day later by a slew of homemade pipe bombs found at the homes or offices of prominent Democrats. One, addressed to the former Central Intelligence Agency director John Brennan, was sent to CNN in NY.
Others targeted included California Sen. Kamala Harris and New Jersey Sen.
Sayoc, a 56-year-old who lived in Aventura, Florida, was accused of mailing explosives to more than a dozen targets last year. Wray also said there were potential DNA matches connecting Sayoc to some of the devices.
Appearing in court in a blue prison jumpsuit, and with his hair pulled into a gray ponytail, he apologised for his actions during an appearance in a US District Court in NY.