When the Singapore Police Force was roped in to help trace contacts of coronavirus cases, officer Tew Meng Hwee put up his hand.
"I wanted to get involved because I know I can contribute," said the Assistant Superintendent of Police (ASP).
ASP Tew, the deputy officer in charge of the Specialised Crime Branch, knew that the police had been involved in contact tracing during the outbreak of the severe acute respiratory syndrome in 2003, and so was prepared to help out this time round.
The Ministry of Health (MOH) is overall in charge of contact tracing operations and the police are called in to help in some cases.
Where the "activity log" of a patient is incomplete and further verification needed, the police will come in to support MOH, said Senior Assistant Commissioner of Police Lian Ghim Hua, the 2 Deputy Director of the Criminal Investigation Department (CID).
The structure of contact tracing goes like this:
The MOH carries out what is known as "backward tracing" of the movements of a patient for the two weeks prior to him getting symptoms. This will identify links to other cases and potential sources of transmission.
MOH officers also do "forward tracing" to identify who the patient had mixed with after getting symptoms. These people may need to be quarantined and tested if unwell.
Over at the police, several teams perform different roles.
A group at the CID Command Centre coordinates with MOH. A second team focuses on interviewing patients and close contacts to flesh out the patient's activity log.
A third group reviews the data collected, and a fourth group of officers from across the force tracks down the contacts MOH has not been able to reach.
Ms Linda Teo, assistant director of the police's analytics research and technology development, said tech tools like data visualisation and word clouds can help draw links between patients.
This was how the dots were connected leading to the realisation of a cluster at The Life Church and Missions in Paya Lebar.
ASP Tan Yong Zhi, the officer in charge of the crime strike force at Marina Bay Neighbourhood Police Centre, said there are mixed reactions when people are told they may have been in contact with a patient.
"Some are fearful, some will be evasive, and some will say, 'No, I'm fine. I'm not sick. I'm feeling okay'," he said.
"We will try to assure them that, don't worry, we are not here to say you are a confirmed case, but just sharing that MOH may be looking for you."
The work comes with some risk but it's all in a day's work for the officers.
ASP Tew, who has gone down to interview patients, said: "My wife wants me to clean myself first after the operation before I go home, so I will do that diligently."