The letter tested positive for ricin, a deadly poison.
On Wednesday, officials confirmed that a letter addressed to President Barack Obama tested positive for ricin—a potentially fatal poison, reports NBC.
An off-site White House mailing facility intercepted the letter. It also happens to be "very similar" to one mailed to Republican Senator Roger Wicker of Mississippi this week.
Despite knowing who may have sent the harmful letters, no arrests have been made—authorities are awaiting more test results.
If ricin is touched, it can cause a rash. But if the poison is inhaled it can cause breathing difficulty, fever and death. There is no known antidote for the poison.
Officials confirmed that filters at a different mail facility tested positive for ricin. FBI officials believe the letters are in not connected to the Boston bombings.