CASE CRACKED:

 This is a letter sent by The Monster with 21 Faces gang that was received on April 23rd 1984. It was sent to both Sankei and Mainichi newspapers as well as the Koshien police station.

English Translation:
”To police fools. You shouldn’t lie. If you lie, you steal. I also sent this to the Koshien police. Why are you lying. Don’t hide things. Why are you complaining? You guys are having such a hard time, so I will give you a hint. I entered the factory from the side staff entrance. The typewriter we used is PAN-writer. The plastic container used was a piece of street garbage.
Monster with 21 faces”

Japanese Text:
けいさつの あほども え
おまえら うそ ついたらあかんで
うそは ドロボーの はじまりや
ちょうせん状は 甲子えん けいさつえも
おくったやないか かくしたら あかん
なきごと ゆっとる ようやから
また ヒント おしえたろ
工場えは 通用門から はいった
タイプは パンライターやポリ「よおきは
ひろいもんや
かい人21面相

On the envelope, the sender was listed as, "Abductor". With no stamp affixed, the postmark was set in Kawachi, East Osaka, two days prior on the 21st.

An image of the actual letter and envelope can be seen here.

The information gathered is presented in an 8 episode podcast, and is set to release on November 17th 2020 on all major podcast platforms and at www.TheMonsterWith21Faces.com as well as the website www.DarqArt.com.

The RSS feed is: https://feeds.fireside.fm/themonsterwith21faces/rss

Please look us up on all social media so you will be notified when the show begins airing.

YouTube - https://www.youtube.com/channel/UCmcv1rfK39psLiYWxlTtlWg
Twitter - @Monster21Faces
Instagram - monster21faces - https://www.instagram.com/monster21faces/
Facebook - @TheMonsterWith21Faces - https://www.facebook.com/TheMonsterWith21Faces

Or send any questions or info to me at 21monsterfaces@gmail.com