According to Weekly Shonen Jump, the second season of Kuroko no Basket
The series of threatening letter cases aimed at Kuroko no Basket has not been settled yet. Although the Tokyo Metropolitan Police has been investigating the case since last October, it has come to a standstill because the culprit apparently has no personal relationship to the author. The threatening letters have been found to be sent to more than 50 places within Tokyo. According to the police, the solution sent to Sophia University along with the letter contained more than the lethal dose of hydrogen sulfide.
Sources: Weekly Shonen Jump
, Sankei News
Kuroko no Basket 2