FBI Investigates Suspicious Letters Containing Unknown Substance Sent to Senators and Election Offices Across the US

The investigation

The Federal Bureau of Investigation and the law enforcement arm of the United States Postal Service announced on Thursday that they are investigating a series of suspicious mailings sent to addresses across the country, including congressional offices and state election offices. Some of the letters contained an unknown substance, officials confirmed.

The FBI said it was working with the U.S. Postal Inspection Service on the case, and told reporters that the suspicious mailings had been “sent to various addresses nationwide, including Secretary of State offices and their related election offices,” according to a statement shared with USA Today. The agency said some of the letters contained an unknown substance and that investigators were working with law enforcement partners to respond to each incident and to identify the person or persons responsible.

Brendan Donahue, a deputy chief inspector with the U.S. Postal Inspection Service, said he could not confirm how many letters had been sent, but confirmed that postal inspectors had intercepted some of them. “Some of the letters have contained an unknown substance, and we’re working closely with our law enforcement partners to respond to each incident,” Donahue said. “I can confirm that we have intercepted some of these letters, and they are in law enforcement possession.”

According to USA Today, officials in at least 15 states, including Louisiana, Oklahoma and Ohio, received letters and at least one package containing a white powdered substance. No injuries had been reported as of October 15.

The targets

Among the intended recipients were some of the most prominent Democrats in the U.S. Senate. Spokespeople for Senate Democratic Leader Chuck Schumer of New York, Senator Chris Murphy of Connecticut and Senator Alex Padilla of California said the Postal Service had intercepted letters containing a suspicious substance addressed to their offices, according to Reuters and ABC News.

Senator Kirsten Gillibrand of New York said in a statement on Thursday evening that a letter addressed to her New York City office had also been intercepted by the U.S. Postal Inspection Service. “I am deeply grateful to the postal inspectors for protecting my staff,” Gillibrand said.

Letters addressed to the offices of Senator Murphy and Senator Lisa Blunt Rochester of Delaware were intercepted before delivery, their offices said. A spokesperson for Senator Murphy said the office “was promptly informed of the letter by FBI, SAA, and Capitol Police,” referring to the Senate Sergeant at Arms and the U.S. Capitol Police. “Due to those efforts and various safety protocols, the Senator and staff were not in immediate danger,” the statement said.

Senator Padilla said the episode was “a stark reminder of the very real dangers facing those who serve the public and who help administer our elections,” according to Reuters.

The mailings were not confined to Congress. The National Association of Secretaries of State and the National Association of State Election Directors said in a joint statement late on Wednesday that a series of suspicious letters had been sent to state election offices. Letters bound for several state election offices were intercepted before delivery, including in Pennsylvania, Ohio and Idaho, according to Reuters.

Alarms inside the Capitol

The episode triggered security alerts in both chambers of Congress. The Senate Sergeant at Arms notified Senate offices that the FBI, the Postal Inspection Service and the U.S. Capitol Police had formed a joint effort to investigate the mailings and block further deliveries. But the Sergeant at Arms also warned staff in an email that “some mail may bypass screening and be delivered to its destination,” urging caution with any packages or letters that appeared unusual, according to reports.

The House of Representatives’ sergeant at arms, the House’s chief law enforcement officer, told staff in an email seen by Reuters that some public officials had received letters containing suspicious white powder substances, and said the House was monitoring the situation.

Congressional mail has been routed through off-site screening facilities since the 2001 anthrax attacks, when letters containing anthrax spores were mailed to Senate Majority Leader Tom Daschle and Senator Patrick Leahy. That attack killed five people nationwide and shut down Senate office buildings for months. Since then, congressional mail has typically been irradiated and screened before delivery — making the warning that some letters could bypass screening especially unsettling on Capitol Hill.

Three weeks before the midterms

The timing has drawn particular attention: the investigation comes less than three weeks before the November 3 midterm elections, which will determine control of the U.S. Congress, according to Reuters. The Postal Service is preparing to handle millions of mailed ballots, a scale of election mail that makes any threat to the mail system politically charged.

The National Association of Secretaries of State and the National Association of State Election Directors said they were working closely with law enforcement and security partners, and had measures in place to respond to potential threats and emergencies while “maintaining essential election operations,” according to USA Today.

The mailings land amid a long-running wave of threats and harassment directed at American election workers. Since the 2020 presidential election, election officials across the country have reported thousands of threats, prompting the Justice Department to establish an Election Threats Task Force in 2021. Prosecutors have since brought dozens of cases against people who threatened election workers, poll staff and public officials — a record that investigators will weigh as they look for motives and patterns in the current case.

Analysis: Why It Matters

This case matters less for what the letters contained — so far, no one has been hurt, and authorities have not said the substance is dangerous — than for what they were aimed at. Mail is one of the load-bearing structures of American democracy: it carries ballots, voter-registration confirmations, and the daily correspondence of government. A coordinated effort to poison that channel, literally or psychologically, strikes at the machinery of elections themselves, and the fact that the letters went to both lawmakers and election administrators suggests the sender understood exactly which machinery they were targeting.

The choice of recipients is the second thing investigators will study closely. Every named Senate target is a Democrat, and several are among the party’s most visible national figures. That does not establish a political motive — the investigation is in its early stages, and no suspect or stated grievance has been made public — but it is a pattern that officials cannot ignore. If the election offices that received letters skew toward particular states, that geography will become another line of inquiry, potentially pointing to whether the sender was trying to intimidate specific jurisdictions ahead of November 3.

There is also a psychological dimension that runs deeper than any single envelope. The 2001 anthrax letters left a permanent imprint on American institutions: Congress rebuilt its entire mail-handling system around the assumption that mail could be a weapon. The Senate Sergeant at Arms’ admission that some mail may bypass screening — even as a cautionary note — will be read by every staffer on the Hill as a crack in that armor. The public-health question of what the substance actually is matters enormously: a hoax powder and a genuine biological agent produce two very different threat assessments, and until laboratories return results, officials must treat every envelope as potentially serious.

For election officials, the mailings arrive at a moment of maximum strain. Local election offices are small operations, often staffed by a handful of full-time workers, and they are about to administer one of the highest-turnout elections of the decade under the constant glare of suspicion. A suspicious letter at a county elections office does not just endanger the people who open the mail; it can delay the processing of ballots, force evacuations, and feed the narrative — already widespread — that the system is under siege. The joint statement from the two national associations of election officials was carefully worded, but its underlying message was plain: they intend to keep the machinery running regardless.

Finally, the case will test the federal government’s election-security apparatus in public. The FBI’s election-crimes posture, the Postal Inspection Service’s screening network, the joint task force with the Capitol Police — all of these systems were built or expanded precisely for moments like this. How quickly investigators identify a sender, how transparently they communicate the laboratory results, and how effectively they distinguish a lone crank from a coordinated campaign will shape public confidence not only in this investigation but in the election it precedes. Three weeks is not much time to get answers right.

What to Watch Next

1. Laboratory results: the most immediate question is what the “unknown substance” actually is — the answer will determine whether this is a bioterror investigation or a mass hoax case.
2. A suspect: investigators are working to identify the sender or senders; postmarks, handwriting, fingerprints and DNA on the envelopes are standard forensic leads.
3. The full target list: authorities have not confirmed how many letters were sent or all of their destinations — the complete picture could reveal a strategy.
4. Screening reviews: expect questions in Congress about how mail could potentially bypass the off-site screening system built after the 2001 anthrax attacks.
5. Election readiness: with millions of mailed ballots about to move through the system, election officials’ security protocols will be under intense scrutiny in the final weeks before November 3.

Sources

• USA Today — “Suspicious letters with ‘unknown substance’ sent to election offices” (Oct 15, 2026)
• Democrat and Chronicle (USA Today Network) — “Suspicious letters sent to Schumer, Gillibrand and other officials nationwide” (Oct 16, 2026)
• Fox News — “FBI probes suspicious white powder letters sent to Schumer, Dem senators as threat spreads nationwide” (Oct 15, 2026)
• Devdiscourse (Reuters wire) — “FBI, US Postal Service investigate suspicious mailings to election officials, lawmakers” (Oct 15, 2026)