Based from what the Newspaper article statement:

“HE WAS both a brilliant student, and a loner who loved his manga comics and World of Warcraft.
David Hartanto Widjaja was in his final year at the School of Electrical and Electronic Engineering and, in the words of a fellow undergraduate at the Nanyang Technological University (NTU), shoo-in “first class honours material”. After all, he’d represented Indonesia in the International Mathematical Olympiad in 2005, and taken part in his country’s National Science Olympics the year before.”

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At that age of a man, he is no longer a boy with unstable emotional feeling who has ended his brilliant mind that way, what would have happened to him, will still become an untold story – which will never be uncovered.

What is the actual fact that might have insulted or intimated “the boy”, and why would he do such thing to an honourable professor whom the article stated as:
“Prof Chan, who joined NTU in 1992 and serves as deputy director of its Biomedical Engineering Research Centre, is said to be in stable condition. The attack stunned Prof Chan’s former students. Ms Stephanie Ng, who graduated in 2007, said Prof Chan “was a fair teacher who was friendly, got along well with students and was not the kind who comes off as stern”.

There’s always one side of the story which is always covered.