Prosecutors admitted they showed the wrong gun to the jury.
At the defense's request, the judge called the trial off.
Torres had been found guilty of shooting Officer Edward Davies in 2013, but that conviction was vacated last year by the Pennsylvania Supreme Court.
Torres then rejected a plea deal by the district attorney's office.
"We look forward to presenting our case against the defendant next month and securing justice of Officer Edward Davies, who continues to heal from his gunshot injuries," said the Philadelphia District Attorney's Office in a statement.
Torres will face his third trial next month.
Officer Davies was in a coma for weeks, and still suffers nerve damage from the shooting.