"This event was probably planned by both of them," Collins said. "What role each played we are still trying to determine." Police are awaiting autopsy results for Alfredo Pimienta, 44; his wife, Georgina Pimienta, 38; and their daughters Priscilla, 17, and Emily, 9.
The bodies of the father and the two daughters were found Tuesday in the swimming pool, and the mother was in the bathtub. Investigators don't know the sequence of how each died, Collins said. No cause of death has been determined.
Collins did not disclose what the parents wrote that led police to determine both of them planned the murder-suicide.
The couple was facing financial difficulties, Collins said without elaborating.
They owned a tow-truck business, Lightning Towing and Transport. The company's business license with the city of San Diego was due to expire on May 31.
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.
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.
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.
"There was no one like her," Jasmund said.
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.
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.
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."
Collins and other police officials did not respond to messages from The Associated Press Tuesday night.
