Olmos reportedly did not want to support a child or his girlfriend, Justina Cornejo, after she told him she would not get an abortion.
Prosecutors say Olmos hired the men to stage a robbery and attack the pregnant girlfriend.
In January 2008, while the couple was parked in a car at a Newbury Park overlook, the men attacked the woman, punching her in the face and stomach.
Cornejo later gave birth to a baby boy, who is now a healthy 2-year-old.
Olmos' defense attorney, Jay J. Tanenbaum of Encino argued Olmos was not properly charged.
Tanenbaum said the California Supreme Court has ruled a fetus seven or eight weeks of age can be the subject of murder, but that in this case the exact age of the fetus was in doubt.
In issuing her verdict, Judge Patricia Murphy said the fetus was measured by a radiologist and that it had visible organs and a beating heart.
Olmos will be sentenced Oct. 21.
Investigations against the two suspect attackers are ongoing. They have not been charged.