Milgram: Jikken Kangoku To Kanshu No Shoujo summary:

Gathered here are five "murderer" prisoners. However, they have all lost their memories.The "crime" they committed is probed by a guard girl, Es, who has also lost all her memories of her past.The past of the "Murderer" is gradually revealed, and the cruel "punishment" that will be inflicted on them――?When you know everything, will you be able to forgive their "sins"――?The long-awaited manga version of the shocking work born from the music project "Milgram" by DECO*27 and Takuya Yamanaka!!