The Alderan Ambassadorial Ship
Darth Vader cares little to nothing about life, truth, justice, rights, or anything that a decent sentient being believes in. Want proof of how little he cares. Let's take a look at his capture of the Alderan ambassadorial ship shortly before the destruction of Alderan.
This was a diplomatic ship that Vader accused of receiving stolen plans from the rebel alliance. His star destroyer chased down and forcibly captured the ship. Vader and his storm troopers boarded it with blaster's blazing. Once the ship was secured, Vader used his mechanically enhanced strength to threaten and torture the crew.
When one such crewman, while in the grip of Lord Vader states that they are on a diplomatic mission, Vader asks him, “If this is a diplomatic ship, then where is the ambassador?” He then breaks the crewman's neck without waiting for an answer. No respect for life, or justice. It would have been just to at least wait to kill him until he'd had a chance to answer the question.
A few minutes later, ambassador Lea Organa is found and brought before him. Not once does it occur to him that this proves that the ship is diplomatic in nature. She professes to being on a diplomatic mission and he accuses her of being a rebel spy.
Even if he believed he was right up to this point, he then shows his disrespect for truth by having his underling send out a false distress signal and informing the Senate that there were no survivors. Why did he do this? Because if the senate had known that one of there number could be held captive by the Empire, the rebellion would have grown stronger. And that was something Vader and the Emperor were quite afraid of.