According to the news release, Aguilar squeezed Megan's rib cage with his hands, causing traumatic injuries that made it hard for her to breathe.
When Aguilar's girlfriend came home, she found the girl limp and struggling to breathe, prosecutors said in the release.
He allegedly insisted that his girlfriend not call the police. He then drove Megan to the Newport Beach hotel where her mother was working, according to the release.
Aguilar picked up the mother and they drove on to the Santa Ana Coastal Community Hospital, where Megan was pronounced dead 15 minutes after her arrival.
She had bruises, lacerations to her body and face, and internal injuries to several organs, including her lungs, liver and brain, according to prosecutors.
According to the D.A.'s office, when Aguilar is arraigned Friday the criminal complaint against him will be amended because, in 2009, he allegedly did a similar thing to a 3-month-old relative.
In that case, Aguilar allegedly squeezed the baby so hard that he fractured her rib cage. That baby survived.
Aguilar is to be arraigned at 10:30 a.m. Friday at the Orange County Central jail.