D.C. police, Fire Department investigators and FBI agents rushed to the Human Rights Campaign headquarters in downtown Washington shortly after 5 p.m. on Memorial Day to investigate a threatening letter containing a suspicious powdery substance, according to police and a Fire Department spokesperson.

Fire Department investigators determined from tests that the substance found on the letter was not hazardous and posed no threat to those who may have come into contact with it, said Fire Department spokesperson Lon Walls.

The letter, which had no return address or name on it, was mailed to nationally recognized gun control advocate Mark Glaze, who had been working for the Raben Group, a lobbying and political consulting firm that rents space in the HRC building, a police report and people familiar with the incident said.

Although Robert Raben, founder and owner of the Raben Group, and Glaze are gay, the threatening letter addressed the subject of gun control and had nothing to do with LGBT rights, said Erika Soto Lamb, communications director for Mayors Against Illegal Guns, for which Glaze serves as director.

Glaze reported that “he arrived [at] his office and retrieved his mail and then went outside into the park area to open his mail,” the police report says. “One of the envelopes opened by [Glaze] contained a threatening message which had a whitish orange substance on the note,” the police report says.

Glaze “left the envelope on the park bench, which was located on the side of the building. The letter was addressed to Complainant 1 [Glaze] but there was no return address or sender’s name,” the report says.

Glaze then called police, triggering the arrival of police and Fire Department members.

“I’ll be working with the FBI and MPD to learn more,” Raben told the Blade in a statement. “I’m grateful no one is physically injured, and sad that hard working professionals have to be concerned about this, but regrettably we do,” he said.

A witness at the scene sent a text message to a friend reporting that police blocked the street near the intersection of 17th Street and Rhode Island Avenue, N.W., where the HRC building is located, shortly after Fire Department and police vehicles arrived on the scene.

The witness also reported that police put yellow crime scene tape around the HRC building as law enforcement officials conferred among each other.

Walls of the Fire Department said the FBI routinely joins D.C. police to investigate incidents in which threatening communications are sent, including those sent with a powdery substance.  He said the substance almost always turns out to be harmless.

“We get about two or three of these calls each day, mostly on work days,” he said. “But we always test it and investigate. We take this very seriously.”

The threatening note sent to Glaze at the HRC building came just over a year after a bomb threat prompted D.C. police to evacuate the HRC building and another D.C. office building in which other national LGBT organizations are located.

For unknown reasons, an unidentified person telephoned the bomb threat to police in Los Angeles, saying a bomb had been placed in the “LGBT building” in Washington, Los Angeles police reported.

As a precaution, D.C. police, when contacted by the LAPD, ordered the evacuation of at least two buildings known to be home to as many as 11 national LGBT organizations – the HRC building and a nearby building on Massachusetts Avenue, N.W.

The latter building is home to the National Gay and Lesbian Task Force, the National Center for Transgender Equality, and other national LGBT groups.

Both Raben and Glaze have worked on LGBT-related issues and national politics for many years. Raben, an attorney, served as a legislative assistant to gay former U.S. Rep. Barney Frank (D-Mass.). Raben later served as an assistant U.S. Attorney General during the Clinton administration before founding the Raben Group in 2001.

Glaze, 42, has worked on a number of issues for Raben Group clients, including campaign finance reform, government ethics, and LGBT-related issues.

Under the auspices of the Raben Group, Glaze recently became a highly visible figure in advocating for federal gun control legislation in his role as director of Mayors Against Illegal Guns, of which more than 950 U.S. mayors are members.

The Washington Blade reported on Glaze’s gun control activities in a profile on him in January, noting that he had been widely featured in mainstream news media outlets, including the New York Times, Washington Post, Politico and the Associated Press as well as in TV news programs.

Lamb, spokesperson for the mayor’s group, said Glaze recently decided to leave the Raben Group to become a full-time staff member of Mayors Against Illegal Guns. She noted that Glaze coincidently had been packing his personal items and moving out of the Raben Group offices at the HRC building at the time the threatening letter arrived.

Glaze “stated…that he was at the location cleaning out his office and is no longer an employee at this location,” the police report says.