The FBI has confirmed that product tampering was to blame for the poisoning of three people who drank from bottles of Coca-Cola laced with a deadly and outlawed rat killer, officials said.

"We know now we are not looking at an accident, we are looking at a deliberate act," Polk County sheriff's spokesman Steve Hulsey said Friday.One person was in critical condition and on life support equipment.

Officials would not discuss any possible motive in the case and said investigators have no suspects.

Chemical tests revealed traces of thallium sulfate, a rat poison and toxic insecticide banned for general use in 1965, in five bottles from which three members of one family drank on Oct. 31.