In this "hard" evidence you refer, Athens have complete knowledge that 1) the plan was put into motion six months ago, and that 2) there has been nothing actually done against anyone (this is assuming that TPF did put the plan into motion, which I would contend).
Let's all put our selves in the situation. If you were informed by that there was a spy plot against you that came to an adrubt end six months ago, the first thing you would do is call in your allies and initiate a sneak attack on the accused? Athens and co made zero diplomatic contact, not so much as to even confirm the content of logs.
The fact that they went to war so quickly and so quietly based on unconfirmed logs says to me that their motive had nothing to do with TPF's alleged spying.