Step one brandish weapon announce robbery and act and sound crazy.
Step two ask people to produce valuables and collect them.
Step three threaten everyone if they move in the next x minutes you’ll come back and start shooting.
Step four run.
At no time do you start killing before robbing.
Step zero: do not plan on doing a robbery on a modern train, where police will be called and be waiting for you at the train station.
You do not board a train with an AK and multiple mags for a simple robbery. This guy planed on shooting a hundred people to death, and then being killed so he could collect his 72 virgins.