We can tell this in the messages that he forces them to write.

我们能从他们被迫写的卡片中看出来
"It's too much."

"我受不了了"
"There's nothing for me here."

"我对那没有留恋了"
"It's better if I leave."

"我走了更好"
We believe this anger stems from his first victim--his father.

我们认为这种愤怒源于首个被害人他父亲
Most likely a local fisherman, definitely an alcoholic,

很可能是当地渔民肯定酗酒
and based on this unsub's level of sadism,

根据不明嫌犯的虐待级别
violently abusive.

他有严重虐待倾向
He's also the first person to abandon the unsub.

他也是第一个抛弃不明嫌犯的人
Walked out on his family, maybe, even wrote a postcard like this.

离家出走可能也写过这样的明信片
So the unsub picked a site of significance to them both,

所以不明嫌犯选了对双方都有意义的地点
a spot known to local fisherman that he turned into his prison.

一个当地渔民熟悉的地方将其作为监牢