The unsub may have had to strangle him

不明嫌犯可能要跟他搏斗
to render him unconscious for the drowning.

击昏他后才能让他溺水
He wasn't just unconscious.

他不只是昏迷
There was pretty intense damage to the trachea.

他的气管受到严重损伤
He was dead before going in the water.

他下水前就死了
But with Nick, he used a blow to the head to incapacitate him,

但嫌犯用击打头部来制服尼克
so this unsub wants his victims alive when he drowns them.

说明他希望被害人活着时溺水
This is the interesting part.

这里很有趣
In all 4 victims, evidence of broken ribs and damage to the sternum

四名被害人的胸骨和肋骨都有断裂
indicate severe chest compression,

表明胸腔受到过严重挤压
yet there are no signs of external trauma.

但却没有外伤
So somebody attempted to perform CPR on these victims?

有人企图对他们实施心肺复苏术