The attacker, a 27-year old Swiss man, released a flammable liquid on board the train and set it on fire, then attacked people with a knife leaving six injured including a six-year old child.
The attack occurred at 14:20 local time.
to set fire - to start a fire with / on something
flammable - able to burn extremely easily and very quickly
aboard (adverb) - on a train, plane, etc.
stabbed - pierced and injured with a sharp object (knife)
on board - while travelling on a train, airplane, etc.