When pressed by U.S. District Court Judge Jed Rakoff however, Sayoc didn't state how he would prevent them from exploding. He had previously pleaded not guilty.
Federal officials called the wave of potential explosive devices sent out in October 2018 a "domestic terror attack" and accused Sayoc of endangering numerous lives.
None of the bombs exploded before being intercepted, and no one was injured.
Sayoc, who lived in a white truck plastered with pro-Trump and anti-Democrat stickers, was arrested in Florida five days after the first device was discovered in Soros's upstate NY mailbox.
The change-of-plea hearing was revealed last week after a phone conference between prosecutors, Sayoc's lawyers and a judge.
The Florida man copped to 65 counts, including use of a weapon of mass destruction and illegal mailing of explosives with intent to kill.
The 56-year-old has been held without bail in NY since his arrest on 26 October, 2018.
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Before a judge, Sayoc said he "never intended for the devices to explode", but acknowledged they could have been set off, according to NBC News.
Authorities say the former stripper sent 14 mail bombs to former Secretary of State Clinton, De Niro and Soros, as well as to the CNN headquarters in NY. Sayoc's plea will avert a trial scheduled for July.
People who knew Sayoc have described his peripatetic existence, saying that he lived for years out of his van while working as a DJ or bouncer at strip clubs.
After Sayoc was arrested, Trump said he "did not see my face on the van" and acknowledged: "I heard he was a person who preferred me over others". One, addressed to the former Central Intelligence Agency director John Brennan, was sent to CNN in NY.
Over several days, investigators tracked the packages to a mailing centre in Florida.
The packages were intercepted from DE to California.
No one was physically injured by the homemade pipe bombs, though Federal Bureau of Investigation officials said each device consisted of roughly six inches of PVC pipe, a small clock, a battery, wiring, and "energetic material" capable of exploding if exposed to heat, shock or friction.
On Thursday, he told the judge he made objects created to look like pipe bombs and filled them with explosive powder from fireworks, fertilizer and glass shards, accompanied by wires and a digital alarm clock.