In the anime there is evidence there were cameras when the police intervened in the Mafia place. Light tells police at the scene they have to keep searching for Mello because none of the gangsters at the scene looks like the drawing of Mello's face made by the girl. It didn't look like they were sending phone pictures. There must have been cameras, and when ...
The YouTube channel Wisecrack has a good video on this topic: The Philosophy of Death Note – What Is Justice?
From the video, I understand that these characters represent these ideologies:
Light/Kira: the end justifies the method. If one has to sacrifice oneself for a greater good, then let it be. He understands that he is a criminal.
L: it's better and ...
A computer can’t kill with the Death Note because it requires the writer to think about the victims face when writing their name.
“The human whose name is written in this note shall die.
This note will not take effect unless the writer has the person's face in their mind when writing his/her name.”
For the same reason he was able to defeate Yotsuba Kira: When he touches a note that he once owned, he temporarely regains/ keeps his memories.
I don't find a reference just now but some time after the first major climax half way through the manga, Light explains to Ryuk/ us that he keeps physical contact to a note using a corset. As long as he touches a ...