Updated 3:56 p.m. | Justice Department and law enforcement officials announced Friday afternoon that a fingerprint and possible DNA evidence led to the arrest of Cesar Sayoc Jr. in the investigation of package bombs mailed to prominent Democrats.

A “latent fingerprint” on an envelope sent to California Rep. Maxine Waters was key to cracking the case, FBI Director Christopher Wray said. The 13 bombs found so far were not “hoax devices,” he said, calling them “IEDs,” or improvised explosive devices.

“There may be more to come,” he said at an afternoon press conference, warning that more bombs may be in the mail.

Watch: Sessions, Wray Discuss Suspicious Packages Arrest