Testimony began Tuesday for the teen accused in the fatal stabbing of a Spring High School student last September. Luis Alonzo Alfaro, 18, is charged in the death of 17-year-old Joshua Broussard.

In opening arguments Tuesday morning, prosecutors told the jury that Alfaro carried out the attack on Broussard and the others as part of a gang retaliation.

They claim Alfaro belonged to a gang called Brown Pride that had been involved in a fight over a girl the day before. Alfaro and others were allegedly looking to even the score.

They may have picked the wrong target. Police sources said Broussard was not involved in the earlier fight and was not a gang member himself.

Crime scene investigators Deputy Joe Noguera with the Harris County Sheriff's Office testified most of the day.

Noguera took photos of Alfaro after his arrest that show blood on his pants and bruises on his face.

Nogerua also walked the jury through a video of the crime scene. When the camera came to rest on Broussard's lifeless body, Broussard's mother and grandmother sitting in the audience hurriedly left the courtroom, sobbing.

Alfaro's defense attorney contends police got the wrong man and that Alfaro couldn't have stabbed Broussard in the few seconds the two were in the hallway together.

Prosecurots have subpoenaed a total of 39 witnesses to testify in the trial.