"The initial analysis indicates that the powder in those particular envelopes did not present a biological threat," Sweeney told reporters. Further investigation of the substance is currently underway, and the probe into the recent incidents is still in its early stages, according to the FBI.
New York Police Department Commissioner James O'Neill echoed the FBI official in this assessment, saying law enforcement officials are not treating any of the explosives as hoax devices.
The two officials did not reveal whether all of the devices sent to multiple targets were the same, and it is unclear if they were made by amateurs or professionals.
READ MORE: Second Suspicious Package Addressed to Rep. Maxine Waters Discovered — Reports
The total number of packages mailed to prominent Democrats, the CNN news network and others is now 10, after authorities intercepted two envelops addressed to former Vice President Joe Biden and one parcel sent to actor Robert De Niro's production company earlier on Thursday. Packages were also sent to former President Barack Obama, former Secretary of State Hillary Clinton, former Attorney General Eric Holder, US Representatives Debbi Wasserman Schultz and Maxine Waters and billionaire liberal donor George Soros.