Police said the couple had dinner at La Parrilla, a restaurant in Boyle Heights, and then went to her uncle's house nearby.
When they left at about 1 a.m., Rebecca took the wheel of their sports utility vehicle and headed toward Whittier.
Soon afterward, a taxicab driver came upon the murder scene on the empty residential street. He told police he found Rebecca Cleland lying on the ground, apparently unconscious. She sat up, however, as he told residents he had summoned the police.
Detectives said she gave a brief statement and then left.
In South Pasadena, Theda Cleland said she awoke in the middle of the night with shooting pains in her head. The next morning, she and her husband heard the news.
"It was devastating," said Harold Cleland, wiping away tears. "I could hardly handle it and I'm barely holding up now. It's a tragic loss."