The letter discovered at Bolling Air Force Base outside Washington comes a week after three others were intercepted on their way to President Barack Obama
We're gonna punish our enemies and we're gonna reward our friends who stand with us on issues that are important to us...
, a U.S. senator and a Mississippi official.
"We've had another incident today, I'm told, at Bolling Air Force Base, the same substance," Senator
Harry Reid... the charismatic senator-for-life from Nevada, currently majority leader ...
told news hounds.
The letter was discovered Tuesday morning during routine screening of incoming mail, said the Defense Intelligence Agency, which is headquartered at Bolling.
Initial tests "indicate possible biological toxins," the agency said in a statement that did not name the toxin.
"Prudent screening methods and force protection measures were implemented to prevent personnel from being harmed," the agency said, adding that it has "maintained normal operations."
Paul Kevin Curtis, 45, was tossed in the calaboose
Yez got nuttin' on me, coppers! Nuttin'!
by the FBI at his home in Corinth, Mississippi last week and charged with threatening the life of the president.
His lawyer insisted Tuesday that they found the wrong man, noting that the FBI could find "nothing" in Curtis's home or on his computer to link him to the letters.
"We have maintained from the beginning ... that Kevin Curtis is absolutely 100 percent innocent," Christi McCoy told CNN.