A 74-year-old man who gained notoriety for robbing a suburban Chicago bank so he could return to a life behind bars should receive more prison time because his 2013 holdup violated conditions of his parole for a 1998 heist, U.S. prosecutors argue in recent court filings.

Walter Unbehaun robbed the BMO Harris Bank in Niles last year wielding a cane but no disguise. He shocked arresting officers later by telling them his plan was to get caught so he could go back "home" to prison.

U.S. District Judge Sharon Johnson Coleman in Chicago sentenced Unbehaun in April to 3½ years for that heist. But prosecutors now want another federal judge to tack on 1½ more years because the holdup violated his parole.

But in a filing Sunday, defense attorney Richard McLeese said it would be unfair to extend his client's sentence after Judge Coleman already concluded 3½ years in prison was sufficient.

"What additional justification exists for an additional 18 months of confinement?" he asked.

Defense filings have said loneliness and mild dementia may have led Unbehaun to conclude that a life in prison was preferable to life outside.

In 1998, Unbehaun was sentenced to an 11-year prison term for robbing a Morton Grove bank. He was released in 2011.

The government filing argues that even with the 3½-year prison term handed down in April, "it is not only possible, but likely, that when released from prison again, (Unbehaun) will commit another violent crime, perhaps to ensure that he is incarcerated for as long as possible."

His rap sheet, they noted, goes back to the earlier 1960s and includes crimes from home invasion to kidnapping.

"Despite his age and health status, a significant additional sentence ... is required," the government filing contends.

McLeese said prosecutors seemed to be asking U.S. District Judge Robert Dow, who is overseeing the parole violation, to impose a lengthy sentence because they believed Unbehaun should have received a longer sentence for the 2013 bank robbery.

"Suppose the situation were reversed and we were the ones dissatisfied with Judge Coleman's sentence, believing it to be too harsh. Could we come to this forum and ask (Judge Dow) to reduce it?" McLeese said.

The next hearing before Dow is set for June 18.