(Photo: AP)

Investigators on Wednesday were trying to determine why a California woman allegedly fatally injured her infant daughter, dropped her young son off a second-story apartment building landing and then jumped herself.

After being medically cleared, Tierra Ortega, 24, was booked for investigation of homicide, attempted homicide and child abuse resulting in death, said Capt. Marcelo Blanco of the Upland Police Department.

Ortega’s booking photo showed her face bruised and scraped with one eye swollen shut.

Her 1½-year-old son remained hospitalized in stable condition with a broken foot and other minor injuries, Blanco said.

“We don’t have a motive yet,” Blanco said.

The tragedy occurred late Tuesday morning in Upland, a small city at the foot of the San Gabriel Mountains in the inland region about an hour’s drive east of Los Angeles.

A neighbor called 911 to report that a child was screaming or crying and then saw the woman was holding the child on a second-story landing, according to police.

“The mother proceeded to release the toddler, who fell to the ground below. Upon officers arriving on scene, they noticed the child on the floor and the mother subsequently jumped from the second story landing head first,” a police statement said.

Police then checked the second-story apartment and found the woman’s approximately 7-month-old daughter inside. She wasn’t breathing.

Her breathing was restored but she died at a hospital, Blanco said.

The cause of her death will be determined but she had a possible skull fracture and internal injuries, he said.

Video from KCAL-TV showed the woman sitting on grass outside the building with her hands handcuffed behind her. One child, strapped to a board, was loaded into a helicopter for the flight to the hospital.

The children’s distraught father was called home from work and police had to hold him back as he struggled to climb the stairs to the apartment.

He spoke to police but “has no idea what led to this,” Blanco said.

The property manager said the family had moved into the unit about a year ago, KCAL-TV reported.

“They’ve always been very quiet,” Kaeleigh Calderon said of the family. “I’ve never heard them arguing, I’ve never heard them bickering.”

Asked about postpartum depression, Blanco said investigators would look into that possibility.