An envelope sent to the White House earlier this week has tested positive for cyanide and further tests will be carried out to confirm the finding, the Secret Service has said. On Monday, an envelope containing an 'unknown milky substance, in a container wrapped in a plastic bag,' appeared at the White House Mail Screening Facility, The Intercept reported. Though initial biological testing yielded negative results, chemical testing returned 'presumptive positive' for cyanide on Tuesday, CNN reported. Secret Service spokesman Brian Leary told CNN that the sample was transported to another facility to confirm the results with a third round of tests. Tests underway: An envelope sent to the White House earlier this week has tested positive for cyanide, the Secret Service said Tuesday, and a third round of tests to confirm the finding will now be carried out . 'Milky Substance:' On Monday, an envelope containing an 'unknown milky substance, in a container wrapped in a plastic bag,' showed up at the White House Mail Screening Facility . The Secret Service will have no further comment because the investigation is ongoing. A law enforcement official said the mail handler suffered no injuries and there were no exposure concerns, Fox reports. An alert identified the return address on the envelope as that of a man with a previous history of incidents with the Secret Service dating back to 1995, The Intercept reports. The man allegedly once sent a package to the White House covered in feces and urine. Then in a 2012 incident, the man sent a package to the White House containing mini alcoholic beverages. Suspicious letters often are sent to some of the country's leading politicians, including the president. Some test positive for hazardous substances while others include threats of death or physical harm. History: An alert identified the return address on the envelope as that of a man with a previous history of incidents with the Secret Service dating back to 1995. He has previously sent letters covered in urine . In June 2013, a West Virginia man was indicted on charges of threatening to kill Obama and his family in a letter that included profanity and racial slurs. A federal judge later dismissed the charges after forensic handwriting analysis conducted by the Secret Service showed that Ryan Kirker, 20, of McMechen, West Virginia, didn't write the letter. Two months earlier, letters sent to Obama, Republican Senator Roger Wicker and Mississippi judge Sadie Holland tested positive for the poison ricin. The letters addressed to the president and to the senator were intercepted before delivery, but one letter reached Holland. She was unharmed. James Everett Dutschke of Tupelo, Mississippi, pleaded guilty in January 2014 to sending the letters and was sentenced to 25 years in prison.
An envelope sent to the White House earlier this week has tested positive for cyanide and further tests will be carried out to confirm the finding . The mail handler suffered no injuries and there were no exposure concerns . Authorities say its sender has been mailing packages to the White House since 1995  including ones covered with urine and filled with alcohol .