CONTRA COSTA, CA — Authorities are still investigating a a suspicious envelope delivered to Congressman Mark DeSaulnier's Walnut Creek office as similar mail continues to trigger evacuations and investigations at congressional offices nationwide.
More than three dozen congressional offices have been targeted, according to reports.
A member of DeSaulnier's staff secured the envelope unopened Friday, after recognizing its description and return address from warnings about threatening mail sent to other congressional offices.
Other envelopes contained threatening letters and a white powdery substance, DeSaulnier said in a statement. He did not identify the contents.
The staff member called local law enforcement and U.S. Capitol Police.
Elsewhere in the Bay Area, investigators have identified some substances mailed to legislators as harmless.
San Jose police determined that the substance delivered to Rep. Zoe Lofgren's office was nonhazardous. Rep. Jimmy Panetta said the powder received at his Santa Cruz office was sugar and flour, and his staff members were initially cleared by medical officials, according ABC7 News.
California Sen. Adam Schiff also announced Sunday that authorities intercepted at least one letter containing a suspicious substance addressed to one of his California offices, UPI reported.
The FBI, U.S. Capitol Police, and U.S. Postal Inspection Service are investigating the mailings.
Law enforcement sources told ABC News last week that preliminary information suggested more than 100 letters apparently containing white powder were circulating through the mail. Investigators were working to intercept additional envelopes.
In a statement provided Monday to Virginia's WJLA, the FBI said it was continuing to work with other agencies to identify whoever sent the letters.
DeSaulnier said U.S. Capitol Police had warned congressional offices about the suspicious envelopes before his staff recognized the one delivered in Walnut Creek.
"Threats and political violence seem to have reached a fever pitch in our country, and I urge my fellow Americans to stand united against such attempts at undermining our democracy," DeSaulnier said in his Friday statement.
"My priority remains the safety and security of my team, and I am thankful for the quick and decisive response," he said. "We remain committed to serving CA-10 residents and will not be deterred from this important work by threats."
Lawmakers whose offices received suspicious mail, or whose incoming mail was intercepted, include:
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