SAN DIEGO -- A family of four that included a 9-year-old girl and a high school senior was found dead Tuesday in a swimming pool and bathtub at their San Diego home, in what police are calling an apparent triple murder-suicide.

The discovery stunned friends and neighbors in the quiet cul-de-sac, who described the four as a hard-working couple, a teenage daughter who was excited for prom and a younger girl who made friends easily.

San Diego police Lt. Ernie Herbert said the suspect was one of the four family members, but he declined to say which one. He said investigators found evidence of a murder-suicide after combing the home, but they were still working to determine a motive.

Maurice Luque, a spokesman for the San Diego Fire-Rescue Department, said earlier that all four appeared to have drowned.

Police identified the victims as Alfredo Pimienta, 44; his wife, Georgina Pimienta, 38; Priscilla Pimienta, 17; and Emily Pimienta, 9.

A relative reported finding the bodies after Alfredo Pimienta called to ask that he visit the home in a quiet southeast San Diego neighborhood, police said. The relative came to discuss a business transaction shortly after dawn.

Police responded to find Alfredo Pimienta and two females -- one apparently the younger daughter -- in the pool and another female in the bathtub. It wasn't immediately clear if the female in the bathtub was the older daughter or the mother.

Neighbors and friends said nothing seemed amiss with the couple, known for logging long hours at work, or their two girls. Georgina Pimienta's stepfather, Jose Villa, said he and his wife picked up Emily from school Monday. He said the family owns a towing business.

Priscilla Pimienta was preparing for college. She was to graduate next month from San Diego's High Tech High School, a charter school that has earned national acclaim for its high graduation rate, said classmate Alex Jasmund.

About 100 people, mostly teenagers, gathered on a San Diego beach Tuesday night to remember Priscilla. The youths held hands around a fire pit and some were seen embracing and talking quietly.

Jasmund said he, Priscilla and two other friends went to a theater Monday afternoon to see the 3-D vampire-hunting movie "Priest," a graphic-novel adaptation. Priscilla met with friends for frozen yogurt after the film to plan for Saturday's prom, including details like ordering a limousine and having a party with about 20 classmates.

Jasmund said everything seemed normal when he saw Priscilla, her parents and her younger sister at a pool party at the home Saturday for Priscilla's friends.

"How can this happen to anyone? Why would this happen to anyone? They don't deserve this. No one does," Jasmund said as he stood with his father outside the ranch-style house with Christmas lights on the garage door.

Marlon Soriano, who lives two doors away, said the family had been renting the home for no longer than two years. They hosted pool parties for relatives in the summer.

"They were a really close family," he said.

The house is one of the few rental properties in the safe, family-oriented neighborhood, said Soriano, 22, who has lived in the area since he was born. New tenants arrived at the home every two or three years.

"We're all pretty close-knit," Soriano said. "We all know each other."

Soriano waved hello to the family but generally didn't talk to them. The younger girl often played with other children in the neighborhood.

"The children were happy," he said. "They always seemed to be smiling."

Soriano said police knocked on his door at 7 a.m. to tell him about the crime scene. Police said the relative called to report the bodies at around 6:40 a.m.