TAIPEI, Taiwan — Taiwanese investigators found that excessive speed caused a train derailment that killed 18 people, and said Tuesday that the train’s driver was considered a possible criminal suspect in the accident.

The derailment on Sunday, which injured 190 other people, happened in the northeastern county of Yilan as the southbound train entered a curve at 87 miles per hour, according to a government task force commissioned by Premier Lai Ching-te. All the train’s eight carriages derailed, with five overturning.

The Taiwan Railways Administration confirmed Tuesday that the train’s driver, surnamed Yu, had manually disabled the automatic train protection system, which ensures the train does not exceed safe speeds. The speed at which the train approached the curve was nearly twice the safe limit for the Puyuma line.

Mr. Yu was placed on a bond of 500,000 new Taiwan dollars, or about $16,100, by a court Tuesday. He is under suspicion of negligence, but investigators are also looking into whether the train was experiencing mechanical problems that may have caused the crash.