Through tears, the wife, Dominique Luzuriaga, of slain police officer Jason Rivera, 22, recalled the horror of seeing cellphone alerts about two officers being shot in Harlem. Her worries grew as she texted and called the former elementary school classmate she married this past October. She got no answer until the call that summoned her to a hospital where he was pronounced dead. Luzuriaga made the comments while speaking Friday morning at her husband’s funeral at St. Patrick’s Cathedral. Authorities are still investigating what motivated the gunman, who was shot by a third officer and later died. Luzuriaga lashed out at new Manhattan District Attorney Alvin Bragg, a Democrat who has instructed prosecutors not to pursue certain cases, including some allegations of resisting arrest. “The system continues to fail us. We are not safe anymore. Not even the members of the service,” Luzuriaga said. Bragg, who had no involvement with …