Police said they received a call from a local hospital about a teen treated for an apparent loss of blood. Hospital workers said she showed signs of having recently given birth, but there was no baby.
Police searched the teenager's home and found the newborn's body hidden in her bedroom closet. The baby girl had suffered severe external and internal trauma, including multiple stab wounds to the torso, according to Fullerton Police Sgt. Andrew Goodrich.
An autopsy is being performed to determine the exact cause of death.
Tovar was released from the hospital Tuesday and was immediately arrested.
Investigators said the teenager was apparently trying to hide the pregnancy from her parents. She was at full-term when she gave birth to the child.
The case is still under investigation and will be presented to the Orange County District Attorney's Office for review.
Tovar is the second young mother in Fullerton this month to be suspected of killing her newborn. Two weeks ago, police arrested 20-year-old Yanira Valderrama for allegedly drowning her baby boy in a toilet and discarding the body in a trash can last September.
The women in both cases are now facing murder charges.
The deaths prompted Fullerton authorities to remind the public of California's Safe Surrender law, in which unwanted newborn children can be dropped off at any fire station or hospital within 72 hours of birth without repercussions.