“I thought the gentleman had had a fit, perhaps. I got the chef de train. We broke the chain and went in. He was – Ah! C’était terrible!’ He buried his face in his hands again.” 

When Pierre Michel, the Wagon Lit conductor, describes his discovery of Ratchett’s dead body to Poirot in Part One, Chapter Five, he expresses shock and despair over the situation. This horrified reaction seems appropriate for the discovery of a murder and suggests that such an act is inherently evil. Of course, Pierre Michel ends up being involved in the plot to kill Ratchett himself, but this initial response distances him from the crime by implying that he views vigilantism as immoral.

“MacQueen’s mouth pursed itself in a whistle. Except that his eyes grew a shade brighter, he showed no signs of shock or distress.”

Poirot informs MacQueen of his employer’s death in Part One, Chapter Six, and he surprisingly displays very little emotion in response to the news. This attitude, while rather nondescript, implies that he does not object to the crime or lament Ratchett’s death. MacQueen even goes on to assume that someone killed Ratchett before Poirot reveals his cause of death, reflecting a kind of eagerness that adds to his unspoken acceptance of the murder.

"In my view, then, this murder is an entirely admirable happening! You will pardon my slightly biased point of view." 

During her initial interview with Poirot in Part Two, Chapter Six, Princess Dragomiroff, who admits to being Sonia Armstrong’s godmother, willingly expresses her relief that Ratchett is dead. The fact that she admits to viewing the crime as a positive turn of events, especially since Poirot knows of her close connection to the Armstrong case, reflects just how strongly she believes in the need for moral justice. Other characters may also acknowledge the necessity of the act, but Princess Dragomiroff’s comment in particular reveals a deep emotional investment in the crime.

"There had been other children before Daisy—there might be others in the future. Society had condemned him; we were only carrying out the sentence."

As Mrs. Hubbard responds to Poirot’s solution of the mystery in Part Three, Chapter Nine, she offers this perspective as to the group’s motivation for collectively killing Ratchett. She suggests that their actions go beyond avenging Daisy’s death and instead have a broader social impact. The idea of saving innocent children’s lives is one that seems honorable and necessary, and the passengers ultimately argue that murder was the only to truly achieve the end result that they, and American society at large, desired.

"In my opinion, Mr. Poirot," he said, "the first theory you put forward was the correct one—decidedly so. I suggest that that is the solution we offer to the Yugo-Slavian police when they arrive." 

This quotation, which appears near the end of Part Three, Chapter Nine, reflects the novel’s final judgement of the twelve passengers who killed Ratchett. By choosing to offer the false, less-incriminating solution to the police, M. Bouc and Poirot wordlessly admit that the passengers’ actions were morally acceptable even if they were illegal. The passengers merely carried out the punishment that the corrupt American legal system failed to deliver, and this perspective suggests that true justice is far more complex than what the law can account for.