Secret Service outside the White House (Getty Images)

An envelope sent to the White House tested positive for cyanide, authorities say.

According to documents obtained by The Intercept, the letter, which was addressed to the White House Mail Screening Facility, tested positive for cyanide after several tests of the “unknown milky substance, in a container wrapped in a plastic bag” found in the envelope.

The letter’s return address is for a man The Intercept says “has a record with the Secret Service dating back to 1995, which includes sending a package covered in urine and feces.” His most recent stunt was sending a package of mini alcoholic beverages in June of 2012.

The letter was received on March 15, but was initially tested negative for cyanide on March 16. However, the chemical testing for the deadly substance returned positive from a chemical testing yesterday.

A request for comment from a Secret Service spokesperson has yet to be returned. We’ll update when more information becomes available.