A suspicious substance mailed to the headquarters of The Church of Jesus Christ of Latter-day Saints is on its way to FBI headquarters in Quantico, Va., for further testing.

FBI agents in Salt Lake City said they received a final report from the state health department on the white powdery substance in an envelope mailed to Temple Square last week. Tests were conducted to ensure it wasn't ricin, anthrax or any other biological weapon.

"It is not any kind of biological agent or toxin or even a new strain," FBI Special Agent Juan Becerra said Monday.

Envelopes with white powder were mailed to Temple Square, the LDS Church's temple in Los Angeles, and a printing press belonging to the Catholic-affiliated Knights of Columbus in New Haven, Conn. Both churches were heavy backers of California's Proposition 8, a constitutional amendment that banned same-sex marriage in that state.

The FBI has labeled its probe a domestic terrorism investigation. Becerra would not say whether the agency had identified any suspects in the case, but reiterated Monday that the FBI had no evidence that linked the threats to Prop. 8 or its opponents.

Many gay rights organizations have also decried the threats.

— Ben Winslow