Manjung district police chief ACP Mohamed Nordin Abdullah said Nga's 76-year-old mother found the notes at about 7.30 am.
She lodged a police report on the matter at 10.15 am.
"This case has been classified under Section 507 of the Penal Code for committing criminal intimidation through anonymous communication, which on conviction provides for a jail term of up to two years or a fine, or both," he said in a statement.
Mohamed Nordin said the case is under investigation and members of the public should not speculate.
He urged anyone with information to contact investigating officer Insp Fariq Nazmi Mohd Mustafa at 013-3317099 to help in the investigation.
Meanwhile, Perak DAP condemned those responsible for sending the notes, saying their action was against the law and the values of society.
Perak DAP is leaving it to the wisdom of the police to investigate the case, it said in a Facebook post.
-- BERNAMA
