The Serpong Stationmaster permitted KA 225 to leave for Sudimara Station without checking the railway condition at Sudimara Station. When the diesel-hydraulic train, KA 225 Rangkasbitung-Jakarta Kota, arrived in Sudimara Station at 6:45 AM (GMT+7) on 19 October 1987, the lanes were all filled with KA 225 in the first lane, KA Indocement in the second lane and a headless freight train. KA 225 was intended to pass KA 220 Patas from Kebayoran to Merak. That meant KA 220 Patas at Kebayoran Station received lower priority for departure. Djamhari, the Sudimara Stationmaster, ordered KA 225's engineer to move his train to the first lane. This order were misinterpreted by the engineer as a go-ahead to continue the journey (compounded by an illegal boarder who hurriedly and wrongly confirms the engineer), and began to move the train. Five minutes later, Djamhari was telephoned by Umrihadi, the officer from Kebayoran Lama Station, informing him that KA 220 Tanah Abang-Merak had departed for Sudimara. Djamhari, shocked seeing KA 225 leaving the station, tried in vain to chase KA 225 while waving the red flag as the train moved at 50km/h. A switcher boarded the rearmost carriage who tries to make it through the train and warn the engineer, to no avail due to the crowded condition. The two crowded trains collided head-on at Km +18.75, causing
telescoping effect which killed most passengers in the carriage immediately behind locomotive. Both locomotives,
Henschel-built
BB303 and
BB306, were also heavily damaged. The death toll came to 139 people, while hundreds more were injured. ==Criminal sanctions==