Authorities have now found two packages addressed to former Vice President Joe Biden that are similar in appearance and contain potential explosive devices that resemble the others sent earlier this week to prominent critics of President Donald Trump and CNN, a law enforcement official said Thursday.
The two packages, discovered at Delaware postal facilities, were removed late Thursday morning, law enforcement officials said.
Earlier Thursday, a suspicious package addressed to actor-director Robert De Niro was reported at the Manhattan building where his production company is based, and its marking and contents appear similar to the other pipe bomb packages, two law enforcement sources said.
The FBI said Thursday morning that the three packages are "similar in appearance to the others."
A manhunt is underway for the perpetrator behind the packages. Law enforcement authorities are treating the series of bombs as a domestic terror matter and are advising the public to remain vigilant.
The motive is unknown, but the recipients are all prominent targets of right-wing criticism and, in many cases, of Trump himself. The package found at CNN's New York bureau in the Time Warner Center was addressed to former CIA Director John Brennan, city and local law enforcement officials said.
Devices sent to former President Barack Obama, Hillary Clinton, former Attorney General Eric Holder, California Democratic Rep. Maxine Waters and Democratic donor George Soros showed the presence of a sulfur substance, which could have exploded, a law enforcement official said.
The devices are believed to be pipe bombs, inherently unstable, and at risk of being set off just by handling.
The FBI's counterterrorism division is leading the investigation Thursday into the packages and the agency says it's possible additional packages were mailed to other locations.
At the White House, Trump vowed Wednesday that "we will spare no resources or expense" to pursue the perpetrator.