Sayoc, 56, is set to be extradited from his home state of Florida to NY where he is scheduled to appear before Manhattan U.S. Magistrate Judge Robert Lehrburger for allegedly sending 15 packages containing homemade pipe bomb devices to prominent Democrats and critics of President Donald Trump.
If convicted, he faces almost 50 years in federal prison.
In support of that argument, assistant prosecutors to Manhattan U.S. Attorney Geoffrey Berman confirmed the November 2 discovery of a 16th explosive device, the second that Sayoc allegedly mailed to Thomas Steyer, the California-based billionaire hedge fund manager and philanthropist who has criticized Trump.
Sayoc allegedly started planning the attacks as early as mid-July while he was living in Florida, prosecutors said in an October 30 letter sent to Florida Magistrate Judge Edwin Torres arguing against bail. He appeared taken aback, however, when Lehrburger noted that Sayoc is charged with assaulting federal officials, among other counts.
He was living in a van covered plastered with stickers of Mr Trump and images of some of the U.S. president's opponents with red crosshairs over their faces.
Sayoc was due to arrive in NY on Monday after waiving his right to a bond hearing in Miami on Friday.
A letter from U.S. Attorney Geoffrey Berman to U.S. Magistrate Judge Edwin G. Torres stated forensic evidence found on Sayoc's laptop shows that he researched his targets, including former President Barack Obama and former Secretary of State Hillary Clinton.
Prosecutors say the most recent crude bomb was recovered on Friday in California, addressed to liberal activist Tom Steyer.
Though she has been estranged from Cesar Sayoc for several years, she said she believes he has been mentally ill "for a long time", making him especially susceptible to the president's frequent anti-media and anti-Democrat remarks.
"This is not how I raised him or my children", Madeline Sayoc wrote in her letter.