Some prisoners already serving time should benefit from a new law that lowers sentences for crack cocaine offenses, but only if their crimes did not involve weapons and they do not have lengthy arrest records, U.S. Attorney General Eric Holder said Wednesday.

Holder made the statements while testifying before the U.S. Sentencing Commission, which is considering whether to retroactively apply lower sentencing guidelines resulting from the new law. As many as 12,000 inmates could see their sentences reduced by an average of three years.

"As years of experience and study have shown, there is simply no just or logical reason why their punishments should be dramatically more severe than those of other cocaine offenders," Holder said of crack offenders, who overwhelmingly have longer sentences than those convicted of offenses involving powder cocaine.

Last year, Congress passed and President Barack Obama signed the Fair Sentencing Act, which reduces penalties for crack cocaine offenses in order to reduce the disparity with powder cocaine penalties. But the act only addressed new cases, not old ones.

Holder told the commission he supports applying the new law to old cases, but not all of them. He said prisoners who used weapons during their crimes or have significant criminal histories should not have their sentences reduced. That could make about 6,000 of the 12,000 prisoners serving time for crack cocaine offenses ineligible for earlier release.

Most of the other people who testified Wednesday also supported making the new crack sentencing guidelines retroactive, including representatives of the American Bar Association and National Association of Criminal Defense Lawyers and former Drug Enforcement Administration head Asa Hutchinson, who was appointed by President George W. Bush.

But not everyone was in favor. David Hiller, vice president of the Fraternal Order of Police, said releasing offenders early would strain law enforcement and hurt communities by putting them back on the streets.

Several relatives of people jailed for crack cocaine offenses also attended the hearing. Among them was Cassandra Baker of Baltimore, whose fiance, David Williams, has served 12 years of a 30 year sentence. Though she doesn't know if the change would help him, she wants to see it happen to help others.

"I'm feeling somewhat optimistic," she said after listening to testimony and questions from commission members.

The commission is expected to rule within the next few months. Four of the six members would have to vote to support the idea. Congress would then have until the end of October to reject or modify the guidelines.