WASHINGTON — U.S. judges overturned a record number of wrongful convictions in 2015 due to increased spending to investigate allegations of false convictions, including for special investigative units in district attorney offices of major cities, a report by the University of Michigan Law School said Wednesday.

The 149 reversed convictions reported by the school’s National Registry of Exonerations is 10 more than in 2014 and more than double the number reported in 2011.

The rising number of exonerations is due to “a long-term increase of the attention and resources devoted to the problem of false convictions,” said project co-founder Samuel Gross, a law professor at the University of Michigan. “On top of that, there is a special concentration of exonerations in counties with very active prosecutorial conviction integrity units.”

Such units are divisions of a prosecutor’s office that work to identify and correct false convictions from previous cases. Prosecutors form these units by reassigning people in their office and requesting additional funding for outside hires.

Former Dallas County District Attorney Craig Watkins established the first conviction integrity unit in 2007, and today there are 24 working units.

For prosecutors, “devoting resources to cases that they prosecuted and finished years, sometimes decades ago” is a relatively new idea, Gross said. “It’s not that prosecutors have never been involved in exonerations, but that they make it a separate function, with employees that do nothing but that, is a new thing.”

The conviction integrity units are responsible for 38 percent of exonerations since 2014, but only some units got big results, the report said. Units from four counties — two from Texas and one from both New York and Illinois — were responsible for 120 of the 134 overturned convictions by integrity units since 2011.

Having an agency review itself to potentially fire employees is tricky, but getting a legislature to agree on a statewide policy and fund an independent commission is not an option yet, Gross said. North Carolina is the only state with an inquiry commission that was approved by the state legislature.

A Conviction integrity unit is “not necessarily the best way to deal with erroneous convictions but it’s the one that’s most effective — at least now,” Gross said.