The little boy died last November, and police say his mother's live-in boyfriend is responsible.
Xavier Hawkins is facing murder and child abuse charges, but one charge was dismissed Monday.
Prosecutors presented the first evidence in the case on Monday.
Investigators believe Hawkins was the only adult in the apartment when the little boy suffered the massive injuries that killed him.
But Hawkins' defense attorney is trying to show the boy's mother may have been there as well.
Syre Bridges lived only 23 months, his life cut short last November by severe abuse.
Three weeks shy of his second birthday, paramedics rushed Syre to the hospital after a 911 call from his mother's boyfriend.
Homicide investigators say Xavier Hawkins also made a call to the boy's mother, Emiley Bridges.
"Xavier told her that Syre was not breathing and the fire department was there doing CPR," Marcus Gray of the Fresno Police Department testified Monday.
The boy died from his injuries soon after.
At the hospital, homicide detective Marcus Gray found Syre covered in bruises from head to toe.
"There were a lot. Multiple bruises on the face, multiple bruises on the arm, the torso, the back, the buttocks area, the legs," Gray said.
Hawkins and Emiley Bridges could only explain a couple of Syre's bruises.
Investigators say Hawkins wouldn't even look at pictures showing the full extent of the boy's injuries, but Dr. Michael Chambliss had to look at Syre to perform an autopsy.
He found a couple old bruises, and a lot of new ones.
Chambliss says extreme physical abuse killed Syre, and the abuse happened just before the boy died.
"I'm saying that the injuries that are fatal, he would not have survived for hours," Chambliss said.
Detectives say Emiley Bridges left her son and Hawkins in their Central Fresno apartment about three hours before the boy died.
But Hawkins' defense attorney says she may have returned.
And, he says, Bridges had a suspicious response when police informed her of Syre's death.
Detectives say there's evidence that Emiley Bridges rode the bus, and shopped at Wal Mart.
Her whereabouts, though, will likely be an issue when Hawkins stands trial.
A judge decided Monday there's enough evidence for Hawkins to face trial on murder charges, but he dismissed sex abuse charges for a lack of evidence.
He's due back in court later this month.