The trial, expected to last until late August, is the first of two for Mark Goudeau. A second trial that includes nine murder counts has not yet been scheduled. Goudeau has pleaded not guilty to all charges.
The prosecutor's sex assault case against Goudeau stems from a massive police investigation of the Baseline Killer, a serial predator named for the south Phoenix street where many of the early attacks took place.
Police say he struck between August 2005 and June 2006.
Goudeau, 42, who lived near where many of the attacks happened, was arrested on Sept. 6, 2006. Police said DNA evidence linked him to the attack on the two sisters a year earlier in a south Phoenix park.
That DNA link promises to be a major point of contention during the trial.
Defense lawyer Corwin Townsend said he is skeptical of the conclusions of government forensic analysts. He wanted to conduct his own test of a key sample, but DNA technicians used up the original swab they say linked Goudeau to the attack.
Townsend called for the case to be dismissed because of the lack of evidence available for an independent analysis. But Judge Andrew Klein rejected that request based on prosecutors' assertions that Townsend could still test a DNA "extraction" from the original police investigation.
Townsend also tried and failed to move the case out of the Phoenix area, arguing that intense media attention has tainted potential jurors. A jury was selected last week after prospective jurors were questioned about their attitudes about rape, race and the police.
Numerous police officers and forensic specialists, as well as the two victims, are expected to testify.
Both sisters now say they recognize Goudeau as their attacker. However, neither identified him in photo lineups before he was arrested and his mug shot was shown on TV. One of the sisters previously identified another man.