Crooked cop who preyed on women undone by tech
CPIB's digital forensic team uncovered evidence of more victims in his devices after he refused to confess
A suspect was being investigated by the Corrupt Practices Investigation Bureau (CPIB) for allegedly using his position to obtain sexual favours from women.
As a police officer, Mahendran Selvarajoo, however, was proving a tough nut to crack.
After hours of interrogation, the staff sergeant, who handles commercial crime at Clementi Police Division, had confessed to only obtaining sexual favours from a woman he had previously investigated.
But while he was being grilled, Mr Chng Tze Wei and his digital forensic team were busy extracting terabytes of data from a computer, three phones and several storage devices seized from Mahendran.
What they uncovered further implicated the 32-year-old, such as his conversations with another woman he had investigated who also provided him with sexual favours.
The CPIB officers went on to discover that the cop had targeted a third victim.
Mr Chng, assistant director of the CPIB's digital forensic branch, told The New Paper in an exclusive interview last week: "There was no reason for him to communicate or follow up with these victims, and that triggered the investigating officer's instincts."
Mahendran was jailed for two years last month.
Mr Fong Wai Kit, senior deputy director of CPIB's investigations operations, said Mahendran, a seasoned investigator, would have had good knowledge of investigation techniques and procedure.
"It is never easy to secure an admission from a policeman," he added.
Still, Mahendran cracked after about 24 hours, and the evidence gathered by the digital forensic team helped CPIB discover more victims and to quickly build a case against him.
Honing in on his messages and multimedia files, investigators were able to confront him with the conversations he had with the second victim, as well as intimate videos of the two victims which he had copied to his devices without authorisation.
This provided a reference point for investigators as they pored over Mahendran's investigation papers and found a third woman he had targeted.
Said Mr Fong: "It was fortunate that we moved in early and prevented a third victim from falling prey to him."
Mr Chng noted that criminals are creating more evidence as digital devices become an integral part of people's lives.
The CPIB recognised this when it introduced digital forensic capabilities in 2004 and has been keeping up with evolving technology trends and finding better ways to analyse the growing mountains of data.
For example, it developed cloud forensic capabilities in 2018 as it recognised the growing use of online storage services such as Dropbox and iCloud, and the potential to find evidence stored in the cloud.
The CPIB has also introduced a new capability in forensic analytics, which halves the time needed to sift through data.
Instead of examining individual devices one at a time, investigators can now examine data across various devices from different subjects through a single consolidated interface to find connections and leads.
Other emerging trends include the use of vault applications, parallel workspaces, and invisible apps to hide evidence.
Payment modes have also evolved, and while many graft cases still involve cash or other forms of gratification like entertainment, the CPIB has long had its eye on cryptocurrency and other fintech innovations.
Mr Chng said: "We are learning in-depth to better get ready for what is to come. I don't want to have a situation where investigating officers don't even recognise potential evidence."
That is why all CPIB investigators are digitally literate, follow technology trends and read the news. This has enabled the CPIB to leverage technology to improve its own processes.
Mr Chng, for example, won a Public Sector Transformation Award last week for a project he worked on with Nanyang Polytechnic students to use blockchain to improve the CPIB's chain of evidence.
Asked about the growing use of privacy and encryption tools, Mr Fong acknowledged the use of such technology by criminals will pose challenges.
But technology is just one piece of the puzzle, he added.
In Mahendran's case, for example, interviewing skills, tenacity and good old detective work were just as crucial.
Said Mr Fong: "Technology has definitely increased our efficiency. "(But) it is the officer's tradecraft and experience that actually allow us to get breakthroughs in our cases."