UPDATE 12:11 PM EST: FBI Confirms that letter tested positive for ricin poison after initial testing, AP reports.
A letter addressed to President Barack Obama contained a "suspicious substance," according to the U.S. Secret Service.
Ed Donovan, secret service spokesman, said that the letter was received Tuesday and intercepted before it reached the White House.
This news comes just a day after a letter addressed to Sen. Roger Wicker tested positive for ricin-a poisonous substance. The Associated Press reports that police have a suspect in mind, according to another senator.
Washington, along with other major cities, have been on high security alert since the Boston Marathon bombings on Monday that killed three people and left more than 180 people injured.
The FBI has launched a massive investigation into the attacks and while no suspect or person(s) of interest have been identified, photos were released that show a mangled lid from a pressure cooker.
It is still unknown whether the bomb was inside the cooking device, but investigators are hopeful that important clues will be uncovered from its emergence.
"Boston is not going to be intimidated by this," said U.S. Secretary of State John Kerry, who is also a former U.S. senator from Massachusetts.
"But we are going to find out who did this. The police work being done is extraordinary. The FBI is remarkable. There is a great deal of forensic evidence. We are hopeful we can bring people to justice," he said in testimony to the House Foreign Affairs Committee Wednesday.
Check back for updates on the Boston Marathon investigation as well as details on the suspicious letter sent to President Obama as they become available.
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Source: CNN