A man has been arrested after a grey Toyota mounted a kerb and struck two pedestrians on Langs Road in Melbourne's Ascot Vale suburb on Saturday afternoon, killing one and leaving the other with life-threatening injuries. The incident occurred outside the Melbourne Showgrounds, which was hosting the Supanova Comic Con & Gaming event (a popular Australian pop culture expo) attended by thousands. Police said the circumstances have not yet been established, and investigators are exploring all avenues, including whether the act was intentional or whether drugs or alcohol were involved; the suspect was apprehended by an off-duty officer with help from members of the public.