This page of our game guide to Control - AWE contains a detailed description of the Dead in the Tracks side mission. By reading our guide you can find out the order in which you have to interact with the objects inside the train.
How to unlock the task: this mission will be unlocked automatically after Hartman is driven away from the Eagle Limited AWE location.
Stay on the balconies where the train has stopped earlier. You can enter the train from the location shown in the picture above.
While in the train, you have to solve a puzzle by interacting with items lying on tables in the right order. Specifically, you have to recreat the events that led to the train crash. Here is the correct order:
The first item - a briefcase.
The second item - a driver's hat.
The third item - a violin.
The fourth item - a meal.
The fifth item - a hammer.
The sixth item - scrap.
If you've made a mistake, then get off the train (pull the string) and re-enter it.
If you have examined the items in the correct order, the train wagon door will open. Walk through them to complete the quest. In addition to crafting materials and modifications, you will unlock a special collectible associated with the train.