According to the Secret Services, an envelope sent to the White House has been tested positive for cyanide. On Monday, the envelope was received at an off-site mail screening facility. In the beginning, biological testing was negative. According to the agency, additional testing which was done on Tuesday gave a positive results for cyanide. Further testing on the sample will also be conducted.

The Secret Service looks after security of President Barack Obama. According to the agency, investigation is still being carried out. Generally, suspicious letters are sent to some of the leading politicians of the country, together with the president. So far, some letters have been tested positive for hazardous substances. Many other letters include threats of physical harm and death.

Letters were sent to Obama, Sen. Roger Wicker, and Mississippi judge Sadie Holland in 2013 and those letters tested positive for the poison ricin. The letters addressed to the president and to the senator were intercepted prior to their delivery; however one letter even reached Holland.

In 2014, James Everett Dutschke of Tupelo, Mississippi, pleaded guilty for posting the letters and was sentenced to 25 years imprisonment.