Christopher Ko Zi Jie, 17, who is autistic, is alleged to have committed the offence on board SBS Service 154 along Jalan Toa Payoh on Oct 30 last year.

He also faces four other charges.

One states that he had in his possession one each of self-improvised metal firing device of a pen gun design, flare/smoke grenade made of metal pipe and aluminium firing device of a miniature cannon at a flat in Clementi Avenue 3 the same day.

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