Said this before, but I am pretty sure hasegawa is the accomplice as he also misdirected them in chapter 28. Some things maybe a few missed in their first read:
- They were supposed to go left but Hasegawa instructed the fat one to go right during the cross
- He was the one who suggested that the fat guy went to the front. He veiled it as "to go at his pace" but he surely did it because he knew that of the people in the group he wouldn't notice it was the wrong way and just go along with it since Okajima follows whatever he is told.
- He was the one who put miyashita in front before the crab walk, again because of "to go at his pace because of his feet". This in turn means he put the person with the lowest mobility and who was most suceptible to cold in front, making him an obstacle for their group while the monkey tried to kill them.
As for wheter hasegawa is the current monkey... Who knows. I don't remember it well, but I thought he was there during the cabin fight between saotome and the monkey so I am unsure if the blood we saw was from Hasegawa who was injured or the real monkey following them.