The letters were sent via the Postal Service to Scientology properties in Hollywood, the San Fernando Valley, Santa Monica, Glendale and Tustin. Police shut part of Glendale's busy Brand Boulevard for two hours before sounding the all-clear, while 60 people were cleared from buildings in Tustin, authorities said.
"Initial field testing by LAPD indicates the powder is harmless," said FBI spokeswoman Laura Eimiller. "However, further testing will be conducted. We will also work to assess what threat, if any, was associated with the mailings and determine whether any federal statutes were violated."
The Church of Scientology had no comment about the incidents. The mailings come after a cyber attack last week on the Church's website. Authorities said there was no evidence that Wednesday's mailings were connected to the hacking.