Before they pass away, each of the victims left a clue that could help Detective Maeda solve the mystery.
Renacchi
Rena wrote three lines with her thumb, fashioned similar to the letter "N", which was debated over if it was really an "N" or a "Z" that she wanted to write. After closer inspection by Mayu and Atsuko, they have found that it was really "IV", the roman numeral version of the number "4".
The Frozen Idol
[To be added]
The Stabbed Cyborg
LOVE4W (Manga)
[To be added]