What happened
On February 22, 1969, two children, Michael and Annabel Velasco, died after eating bread containing endrin, an insecticide. A third child, Imelda, survived after becoming ill.
The prosecution theory
Lucila Valero was accused of giving poisoned bread to her deaf-mute brother Alfonsito, who allegedly passed it to the children. The case against Alfonsito was dismissed because proceedings were beyond his comprehension, leaving Lucila as the defendant.
Trial and automatic review
The trial court convicted Lucila of a complex crime involving double murder and frustrated murder and imposed the death penalty. On automatic review, however, the Supreme Court found crucial prosecution evidence to be hearsay and criticized the trial judge for relying on an unexpected speculation about Lucila's mental condition.
Supreme Court outcome
On March 19, 1982, the Supreme Court reversed the conviction and acquitted Lucila Valero, concluding that the prosecution had failed to establish her guilt. The underlying poisoning deaths therefore remained without a sustained conviction against her.
Source
Supreme Court, People v. Lucila Valero, G.R. Nos. L-45283-84 (March 19, 1982)