The brutal murder of a 31-year-old woman is being attributed to the tenuous association of the killer's time playing Final Fantasy XIV. These conclusions are being drawn by two German tabloids, according to this Kotaku report. The 31-year-old woman, Katrin M. (the last names of both the victim and the killer are being withheld) was reportedly murdered by 18- or 19-year old Marco F, who stabbed the victim 18 times using a katana.
Munich tabloid TZ is running photos of the alleged killer "cosplaying as his favorite Final Fantasy character." As Kotaku rightly points out, the cosplay character in question is actually Neku Sakuraba from another Square Enix game, The World Ends with You. The game does contain violence but no blood or gore. And even if it did, it is likely that German Government censors would have made Square Enix remove it from the game before it was released.
Another German paper called Abendzeitung pointed to Marco's Final Fantasy XIV profile but that profile indicates that he was not a regular FFXIV player and the game doesn't not have blood and gore in it.
Ultimately it's a conclusion drawn based on the fact that Marco played games with swords in them, but millions of people around the world play video games. Comparing his time with Final Fantasy, The World Ends With You or any other game would be like blaming the brand of soda he drank...