By Karen Anderson, WBZ-TV

BOSTON (CBS) – Former investigators, officers and attorneys call it inconceivable that Whitey Bulger was given immunity, as his attorney claims in his latest filing.

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Bulger’s attorney claims former US Attorney Jeremiah O’Sullivan gave Bulger immunity.

But former federal prosecutor Allison Burroughs says immunity deals must be in writing, and they don’t include violent activity or future crimes.

Bob Long, who spent two decades tracking Whitey Bulger for the State Police, calls the claims ridiculous.

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“Murder? That’s absurd. Young innocent women? that’s absurd,” he said. “O’Sullivan might have been a lot of things, but one thing, it was not in his character to allow this to happen.”

Revelations about immunity emerged through Bulger’s motion to have Judge Richard Sterns recuse himself from the trial. Sterns has refused to step down from the case at this point.

Sterns was the Chief of the Criminal Division of the US Attorney’s Office, and Bulger’s attorney JW Carney says he plans to call Sterns, as well as Sterns’ friend, FBI Director Robert Mueller, to the stand.

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Carney says Bulger will reveal the details when he takes the stand in the trial.