Prison sentences of black men were nearly 20% longer than those of white men for similar crimes in recent years, an analysis by the U.S. Sentencing Commission found.

That racial gap has widened since the Supreme Court restored judicial discretion in sentencing in 2005, according to the Sentencing Commission's findings, which were submitted to Congress last month and released publicly this week.

In its report, the commission recommended that federal judges give sentencing guidelines more weight, and that appeals courts more closely scrutinize sentences that fall beyond them.

The commission, which is part of the judicial branch, was careful to avoid the implication of racism among federal judges, acknowledging that they "make sentencing decisions based on many legitimate considerations that are not or cannot be measured."

Still, the findings drew criticism from advocacy groups and researchers, who said the commission's focus on the very end of the criminal-justice process ignored possible bias at earlier stages, such as when a person is arrested and charged, or enters into a plea deal with prosecutors.