Well, being a Joker Game fan I guess I was in advantage on recognizing clues on spy behaviour... and I guess it helps also I tend to obsess over the visual and minor details.

Plus I was always under the belief Tsurumi knew about Kiro prior to the beginning of GK... (though back then I hadn’t anticipated this) and there were other minor things.

So by connecting the dots I ended up with suspecting Hasegawa and Tsurumi could be one and the same.

I wasn’t sure I was right though (and I was expecting we would learn Tsurumi’s past around the end of the manga, not now), it only seemed like a possibility.