But changing how the nation’s more than 16,000 independent law enforcement agencies handle the presentation of suspects to witnesses will be no easy task, many experts say.

Around the country, the notion of change has met with resistance from police officers who remain skeptical about the research and bridle at the idea that they could affect the responses of witnesses, even unintentionally, which studies find is how most influence occurs.

In many communities, lineups are conducted in the same way they have been for decades, although typically these days they involve photos, not actual people. According to some estimates, only about 25 percent to 30 percent of jurisdictions have police departments that have revised their policies to protect the integrity of lineup procedures.

Although some states are studying revisions or require single changes in procedure, only two — New Jersey and North Carolina — mandate the two practices that researchers regard as most important: lineups that are blinded, that is, administered by someone who is not familiar with the suspect and who is not one of the primary investigators on the case; and photo arrays that are presented sequentially rather than as a group. Both practices, studies find, decrease the pressure on witnesses to pick someone and guard against influence.

The idea that human memory is frail and suggestible has gradually gained acceptance among leaders in law enforcement, buttressed by more than 2,000 scientific studies demonstrating problems with witness accounts and the DNA exonerations of at least 190 people whose wrongful convictions involved mistaken identifications. About 75,000 witness identifications take place each year, and studies suggest that about a third are incorrect.