ok, so mc and sc both had a deathnote. the explanation mc came up with for the police was that they unknowingly used the same notebook and mc worked out was what going on. mc also gave sc this explanation. sc believes this explanation. the 1 deathnote was burned by the detectives.
after this mc made a story about a deathnote that became popular and made it seem fictional. by pretending to cooperate with the detectives, risking his life and destroying the decoy he had a police confirmed alibi and weight of innocence. the fictional deathnote story also added an element of disbelief which would deflect suspicion. as the police are aware of his history his knowledge is not suspicious.
thanks to this groundwork he is now free to use his deathnote as he likes. he'll likely use the survey as a guide to determine his support base. if he makes the surveys results public that furthers the aspect of plausible deniability.
Wait what happened at the ending I didn't understand at all
I'm bamboozled someone pls explain the ending Σ(っ°Д °;)っ