SEATTLE (AP) _ Authorities still don't know who laced Sudafed capsules with cyanide a year after three Washington state residents were poisoned, but the FBI says it's still on the case.

''We'll stay on it as long as we need to get as much evidence as we need,'' said bureau spokesman Dave Hill. ''If it takes five years, we'll work on it for five years.''

A year ago Sunday, cyanide powder packed into a Sudafed 12-Hour cold capsule sent Jennifer Meling of Tumwater into seizures. The 28-year-old schoolteacher lapsed into a coma but survived.

Two others weren't as fortunate. Within three weeks of Meling's poisoning, 40-year-old Kathleen Daneker of Tacoma and 44-year-old Stanley McWhorter of Lacey died after taking tainted Sudafed capsules.

The deaths triggered a nationwide recall, a lawsuit against Sudafed manufacturer Burroughs Wellcome, a public-awareness campaign against product tampering and the FBI investigation.

Although a year has elapsed, Hill said, the case isn't hopeless. Eighteen months passed after two people died in a 1986 Exedrin tampering case before the arrest of Stella Nickell of Auburn, who was found guilty and sent to prison.

Daneker's and McWhorter's survivors sued Burroughs Wellcome, based in Research Triangle Park, N.C., claiming the deaths could have been avoided had the company not waited a month after the first poisoning to issue an alert.

Company attorney P. Arley Harrel said authorities believed the Meling case was an isolated incident.

''At the time it didn't look like it was an on-the-shelf tampering where the public safety was at risk,'' Harrel said.

The case is set for trial in Tacoma in September.

Sudafed 12-Hour returned to stores in late April as a coated tablet that's less vulnerable to tampering.