New York City Mayor Michael Bloomberg and New York Police Department Commissioner Raymond Kelly. (Photo by Spencer Platt/Getty Images)

A letter containing the deadly poison ricin was mailed to a gun control advocate with ties to New York Mayor Michael Bloomberg at an office in the Human Rights Campaign building in D.C. A similar letter was reportedly sent to President Obama.

“Anonymous threats to Mayor Michael R. Bloomberg in letters opened in New York City on Friday and by the director of the Mayors Against Illegal Guns in Washington, D.C. on [Monday] contained material that when tested locally, preliminary indicated the presence of ricin,” NYC Police Department Deputy Commissioner Paul J. Browne said in a statement. “The writer, in letters, threatened Mayor Bloomberg, with references to the debate on gun laws. Civilian personnel in New York and Washington who came in contact with the opened letters remain asymptomatic.”

The director of Mayors Against Illegal Guns is Mark Glaze. He was working out of the Raben Group’s office in the Human Rights Campaign building Monday when he received the letter, according to the Washington Blade, the first outlet to report this information. Glaze opened the letter while sitting on a bench near the building, which is located at 1640 Rhode Island Ave. NW.

Erika Soto Lamb of Mayors Against Illegal Guns, who provided some of this information to the Blade, declined to comment to DCist citing the ongoing investigation. Request for comment from the HRC has not been returned.

The HRC building remained open this week, an employee who works there told DCist. The organization spoke to Dr. Brian Amy, a D.C. Department of Health senior deputy director of health emergencies, who assured them that the building is safe to occupy, according to an email sent to that employee.

Material from the letter tested “weakly positive” for ricin, according to the email.

Sources told NBC4 that a third letter, similar to the ones sent to Bloomberg and Glaze, was addressed to President Obama. It was sent to an off-site facility and did not reach the White House.

This is Obama’s second ricin scare this year. A letter containing the substance, made from the castor oil plant, was also mailed to Senator Roger Wicker.