Former University of California at Berkley math professor Theodore John Kaczynski is escorted into the federal courthouse in Helena, Mont., Thursday, April 4, 1996.
The FBI says it's investigating whether Unabomber Ted Kaczynski was involved in the 1982 Tylenol poisonings case that killed seven people.
Kaczynski wrote in court papers filed in federal court in California last week that prison officials conveyed a request from the FBI in Chicago for DNA samples.
Chicago FBI spokeswoman Cynthia Yates confirmed Thursday that the agency has asked for Kaczynski's DNA. She says he's refused to voluntarily give a sample but declined to say whether the agency could compel him to provide one.
The Tylenol case involved the use of potassium cyanide and resulted in a mass recall. Kaczynski says he has never possessed potassium cyanide.
Kaczynski is serving a life sentence after pleading guilty in a Sacramento courtroom in 1998 to setting 16 explosions that killed three people.
Among the victims were Sacramento computer store owner Hugh Scrutton, California Department of Forestry president Gilbert Murray and Burson-Marsteller executive Thomas J. Mosser.