(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 Manchester halfway house when he was supposed to be Sunday afternoon, according to the New Hampshire Department of Corrections.
Authorities say they are considering it an escape because Eisenberg did not let anyone know he was leaving, as he is required to do. They said he is not considered armed or dangerous.
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. He is eligible for parole in August.
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 and Janet DiGiacomo contributed to this report.