i'm just gonna straight up say that yamoto hideo's 'homunculus' is my favourite manga of all time and a hidden gem of the psychological genre, so if you haven't read that, give it a go and perhaps let me know what you think of it. otherwise, i'd also greatly recommend naoki urusawa's 'monster' and '20th century' boys, keigo higashino's 'heads' and shinichi sakamoto's 'kokou no hito'.
I second Homunculus, it really is a masterpiece that you should read if you haven't. I also recommend Tsumi to Batsu : A falsified romance and Kimi no Knife
I second Homunculus, this one is a masterpiece. I recommend Kimi no Knife, Tsumi to Batsu: a falsified romance and Tomodachi Game (this one is still ongoing unlike the other two)
it's the only genre I read besides yaoi and shounen ai (〜 ̄△ ̄)〜