[6] Siu has served in various posts of different job nature, mostly frontline operational units as well as criminal intelligence-related duties and Personnel Wing.

In January 2017, Siu was promoted to the rank of Assistant Commissioner of Police when he was then assigned to command the Personnel Wing.

In November 2018, Siu was promoted to the rank of Senior Assistant Commissioner of Police, taking up the post of Director of Operations.

In October 2021, Siu declined to meet with Amber Poon's mother when she invited him to join her for a press conference.

[9] On 5 January 2022, Carrie Lam announced new warnings and restrictions against social gathering due to potential COVID-19 outbreaks.