Robert Quiroz faced four charges in connection with the death of his three-month-old son, Roman.
A jury found the 25-year-old guilty of second degree murder, as well as child abuse causing death.
They found him guilty of injury to a child for breaking Roman's ribs, but they found him not guilty of injury to a child for a prior injury to his arm.
Robert's family backed him throughout the trial.
They shed some tears Monday afternoon, and left without talking to the media.
But Action News heard from a sister who is still defending the ex-marine.
Quiroz closed his eyes when he heard the jury's decision on his fate.
He kept his composure and had nothing to say, but his family and his attorney's assistant cried for him as the verdict came down.
"You know he really didn't have any words," said his defense attorney, Michael Idiart. "He was more concerned with my assistant and how she reacted."
It took five years for Quiroz to stand trial, and two weeks to get through all the evidence, but only four hours for the jury to reach their verdict.
In the end, they sided with prosecutors who said Robert squeezed his son Roman's ribs so hard, he broke ten of them, then threw the boy into something so hard, the 3-month-old suffered a complex fracture to his skull.
"I think the forensic evidence was strong and I think there was a great investigation right from the beginning of this case," said prosecutor Mike Frye.
For Quiroz, the journey from the uniform of a Marine to the prison uniform he'll wear from now on has been a long one.
In 2006, his wife died in childbirth on the day Quiroz arrived in Iraq.
He rushed back to Fresno and took over childcare duties for the newborn Roman, and his older sister.
As Robert's sister, Catalina, posted on the ABC-30 Facebook page, family members always believed he had nothing but love for his kids and would never hurt them.
But even his own attorney wasn't surprised by the verdict -- disappointed, but not surprised.
"I knew this was a difficult case," Idiart said. "You have an infant victim and my client always admitted he delivered the death blow."
Idiart told jurors his client was guilty of involuntary manslaughter, but not murder -- a losing argument in the end.
Roman's older sister is alive and well, living with her mother's family. Her father will be sentenced in December.
If he gets the expected sentence of 34 years to life, he'll be eligible for parole for the first time at the age of 45.