Welcome, enter your question. Please start with words like "Who, What, Where, When, Why, How, etc..."

What would you be referring to?

If the question is referring to various PV's portraying Rin Kagamine as a killer, then that can not be answered by the wiki correctly. However, it should be noted that PV's created by fans or producers are not official or acknowledged as such by the respective company. Fanmade music videos and fanart are a way for people to create their own version of a Vocaloid character.

In the Japanese fandom it appears to portraying characters as a murderer (or Yandere) is common and at times done humorously. In particular when there is a deep storyline involved.

Answer: Crypton has never confirmed that Rin is a serial killer. The personalities of the Vocaloid are basically the decisions of the user. Even if Rin was a yandere, the users would be left to decide why. I hope that this answers your question! :)