A thief stole mail belonging to residents at six blocks of flats in Woodlands after a postwoman left a SingPost trolley unattended while using a restroom.
The theft took place at Block 734, Woodlands Circle last Thursday.
A SingPost spokesman said the postwoman did not take the postal items to the restroom three blocks away as it was raining heavily and she did not want them to get wet.
She tried to conceal the trolley with pieces of wood.
The postwoman discovered the trolley missing at 4.30pm and made a police report after conducting a search.
The SingPost spokesman said yesterday that it was "working closely" with the police and has notified affected residents.
It will also take disciplinary action against the postwoman, an employee of 17 years, for breaching "an established standard operating procedure" which forbids postal staff to leave mail unattended.
Ordinary mail is not tracked by Sing- Post so it cannot tell what items had been taken.