The search for suspects in the attempted delivery of packages resembling bombs to prominent Democratic political figures continues as investigators try to figure out who sent the suspicious packages and why.

The number of potential crime scenes reached 10, as law enforcement officials found more packages addressed to high-profile figures, including former Vice President Joe Biden and Hollywood actor Robert De Niro, an outspoken critic of President Donald Trump.

Law enforcement officials are treating the mail bombs as a potential act of terrorism, as investigators zero in on Florida as the place of origin for some of the devices.

Among the others targeted were former Secretary of State Hillary Clinton; former President Barack Obama; former CIA Director John Brennan (via CNN’s offices in New York); billionaire liberal political donor George Soros; former Attorney General Eric Holder; and Rep. Maxine Waters, D-Calif.

None of the bombs actually exploded, which experts consider significant, given that some traveled through the postal system—a bumpy journey. NBC reported that some of the bombs analyzed were “flawed and not capable of exploding,” but whether that was a design flaw or intentional is not yet known.

The suspicious powder found in the packages sent to New York addresses, including to the CNN offices, “did not contain a biological threat,” FBI Assistant Director William Sweeney said at a press conference.

Many in the media spent the day suggesting Trump bears responsibility for the mail bombs, despite not yet knowing who the perpetrator is or his or her motives. Some media organizations such as CNN cited the rhetoric Trump has used about the intended recipients.

“There is a total and complete lack of understanding at the White House about the seriousness of their continued attacks on the media, and especially the White House press secretary should understand their words matter,” CNN’s president, Jeff Zucker, said in a statement.

“Thus far, they have shown no comprehension of that,” he said.

Trump condemned the mail bombs Wednesday, at the White House and at a later rally in Wisconsin.

“Acts and threats of political violence have no place in the United States of America,” the president said.

In a tweet Thursday morning, he blamed the “anger” in American society on what he regards as “fake news” and called on the mainstream media to “clean up its act, FAST.”

Quoting that tweet, Brennan, one of the Trump critics targeted by the mail bombs, said: “Stop blaming others. Look in the mirror.”

As the investigation continues, federal agencies are reviewing security protocols for former Cabinet-level officials and other high-profile figures.