A lot of the air has gone out of the criminal case against Pacific Gas and Electric Co. with federal prosecutors’ stunning decision this week to slash the maximum potential fine by nearly 99 percent — from $562 million to $6 million — if PG&E is found guilty of violating pipeline-safety laws.

The action Tuesday came at a highly unusual time, during jury deliberations after a 5½-week trial. It has led some, like a Stanford criminal law professor, to question the value of the prosecution, even if California’s largest utility winds up as a convicted felon.

“Had some agency of the (federal) government gone after them for a large amount of money, you still would have had some stigma or deterrence,” said Robert Weisberg, co-director of Stanford’s Criminal Justice Center. “Now it seems like filling up air time to get to some resolution. It’s hard to figure out what the government has gotten out of this.”

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Weisberg, the Stanford law professor, said the dramatic reduction raises questions about whether the prosecution had a “well-thought-out strategy” in taking the case to trial.