FREMONT — The white substance mailed to a Fremont courthouse employee this week was not anthrax, authorities said Wednesday.

When the substance was tested at the courthouse Tuesday afternoon, local firefighters could not rule out the possibility that it was anthrax. By law, they had to send it to the state-run lab in Berkeley, where it was tested late Tuesday and determined not to be the potentially dangerous substance, said Sgt. J.D. Nelson, spokesman for the Alameda County Sheriff's Office, the agency handling the investigation.

Although authorities ruled out anthrax, they had not determined Wednesday what the powder was, Nelson said. Further testing was being completed at the lab on Wednesday, but it was unclear when the results will be made public.

An employee at the Fremont Hall of Justice received a letter Tuesday afternoon and before opening it, realized that it looked suspicious. He contacted

sheriff's deputies who work at the facility and the county bomb squad was summoned, Nelson said.

The bomb squad inspected the envelope to make sure it was not explosive, and then opened it. They then called the Fremont Fire Department and its hazardous materials team after finding a heavy powder in the envelope.

Nelson said detectives have not been able to determine where the letter came from, and that their investigation is on hold until the envelope that contained the substance is released from the lab.

Staff writer Ben Aguirre