There was no immediate claim of responsibility.
Thirteen top Democrats and Trump critics were the targets of mailed pipe bombs this week but calls for political unity over the attacks swiftly unraveled, as Donald Trump reverted to blasting the media and seemingly giving credence to rightwing conspiracy theories. "We must show the world that we are united together in peace and love and harmony as fellow American citizens".
He added: "The hypocrisy this morning of watching Trump saying we've got to stop this endless hostility and how we speak negatively about others".
The parcel intended for Holder ended up rerouted to the return address printed on all the packages - the Florida office of U.S. Representative Debbie Wasserman Schultz, who formerly chaired the Democratic National Committee, according to the Federal Bureau of Investigation.
"You gotta calm it down", said Anthony Scaramucci, a prominent Trump supporter who briefly worked in his administration.
FBI Director Christopher Wray told the news conference that fingerprints on a package sent to Representative Maxine Waters belonged to Sayoc. Each bore a computer-printed address label and six "Forever" postage stamps.
The official says each device also had a small battery, similar to a watch battery.
The discovery of pipe bombs targeting prominent Democratic politicians and CNN is raising the threat of election-season violence largely unknown in the US - and prompting uncomfortable questions about the consequences of leaders' increasingly vitriolic rhetoric.
The US mail bomb scare has widened as police seized three more suspicious packages - two addressed to former vice president Joe Biden and one to actor Robert De Niro.
The package sent to Biden was found at a postal facility in New Castle, Delaware, while the package sent to De Niro's Manhattan office was called in by a building worker who was anxious about a suspicious package that arrived days earlier.
Brexit: EU offers border compromise as Cabinet to get weekly updates
The EU also volunteered to extend the post-Brexit status quo transition period by a year until the end of 2021. May has proposed that the whole of the United Kingdom should remain in the EU customs union .
"We will prosecute them, him, her, whoever it may be, to the fullest extent of the law", he said at a White House event.
An FBI statement said the other packages consisted of a manila envelope with a bubble-wrap interior containing "potentially destructive devices".
The targets were figures frequently maligned by right-wing critics.
Trump did just about the bare minimum expected after the attempted attacks using improvised explosives on two of his predecessors, several other prominent political critics and the NY offices of CNN.
In a written statement, CNN President Jeff Zucker decried what he called "a total and complete lack of understanding at the White House about the seriousness of their continued attacks on the media". "Thus far, they have shown no comprehension of that".
But Trump's response to the discovery of the 10 suspicious packages, including those intended for former President Barack Obama and former Secretary of State Hillary Clinton, has been in large part another way to air his grievances about the way he and his administration have been covered.
"I think Republicans feel that the increasing radicalization of the Democratic Party, that the growing support for Medicare for all - without a realistic plan to pay for it - also provides an opportunity when talking to a lot of voters who are trying to make up their minds right now", Steel said.
Some in the crowd began to yell "Fake News", a staple at any Trump rally, while one person shouted "CNN Sucks!" Some journalists now travel to Trump rallies with security personnel, for example.
Trump's critics charged that his inflammatory rhetoric against Democrats and the press created a climate for politically motivated violence. "I have to say at the beginning New Yorkers have been absolutely outstanding in how they've dealt with this".
"I'm afraid that has to land back at Donald Trump's doorstep, because for two years now he's been going round calling these people enemies of the state, getting his people to shout lock her up, attacking Barack Obama", Mr Trundle told talkRADIO's Julia Hartley-Brewer. "Have you ever seen this?"