NATIONAL NEWS (CNN) — Leeland Eisenberg is missing yet again.
The 52-year-old New Hampshire man, who took hostages six years ago at one of Hillary Clinton's campaign offices, was not in his halfway house Sunday afternoon, according to the New Hampshire Department of Corrections.
Eisenberg is not considered armed, authorities say. He is eligible for parole in August.
This is at least the second time Eisenberg has left authorities wondering about his whereabouts.
He was released in 2009 after serving two thirds of a three-year sentence. But in February 2010, he violated his probation by cutting off his GPS tracking bracelet. He was arrested about a day later and eventually received a new sentence of 3 1/2 to 7 years.
Eisenberg has a history of mental illness and substance-abuse problems, authorities say.
In 2007, he entered Clinton's campaign office in Rochester, New Hampshire, with road flares strapped to his chest. He claimed he had a bomb, and he held several hostages for five hours. Clinton was in Washington at the time.
In an interview with CNN in 2007, Eisenberg said he took the hostages to raise awareness about mental health issues.
"I wanted to sacrifice myself for mental illness and bring about the discussion about mental illness," Eisenberg said. Furthermore, he said, "I wanted the police to kill me."
He was convicted of multiple counts of kidnapping, criminal threatening and false reports of explosives.
CNN's Elwyn Lopez contributed to this report.