She lost her hair, apparently from cancer treatment. She is believed to have lived out of her van and used a Beverly Hills post office box. She has had previous run-ins with the law, mostly over traffic mishaps.

Little else is known about Kathryn Schoonover, who is suspected of trying to mail cynanide packets that looked like free samples of nutritional supplements.Was she trying to prove something? How and why did she select the alleged targets, mostly police and medical professionals? Are any previous poisoned mailings out there?

Late Monday, authorities still had no motive for the alleged attempted murders by mail, said Detective John Vernon of the Los Angeles County Sheriff's Department. Schoonover, 50, was to be arraigned Tuesday afternoon.

Deputy Bob Killeen said Schoonover denied mailing any cyanide-laden letters.

U.S. postal officials have sent warnings to the service's employees across the country. "We're not taking any chances," said Postal Service Inspector George Marsh.

Post offices were told to look for envelopes matching the description of those seized. They are off-gray in color and bear no return address. Postal inspectors say anyone who gets such an envelope should leave it alone and contact the local post office. There have been no known deaths.