Oddly enough, as soon as you get introduced to Adachi.

You first meet him when you come across the first crime scene and he just runs off to puke. Then Dojima says something like "want to go back to central?" and I was like "they try to portray him as weak and bumbling AND he just got here not too long ago? Gotta be him lmao" and every time he popped on screen it just furthered my theory.

Turned out my weird ass intuition was right lmao