WACO, Texas -

A grand jury has declined to indict three Waco police officers who responded to a gunfight involving rival biker gangs, Waco police said Wednesday.

The incident, which was reported in May 2015 between members of the Bandidos and Cossacks gangs, left nine people dead and 20 injured.

The police statement didn't indicate what actions of the officers the grand jury was asked to review. Ballistics reports seen by The Associated Press show that four of the people who were killed were struck by bullets of the same caliber of rifle fired by Waco police.

More than 150 bikers were indicted after the shootout on a charge of engaging in organized criminal activity.