In other words... you don't have any.
There are only two reasons:
1.) Manning stopped being "suicidal" (a state assumed by the defense dept. before detainment)
2.) The defense department was feeling pressure from the U.N. and had to let him go
Since there is no evidence prior to his detainment that he was "suicidal", it stands to reason that his 8 month stay for the same reason was also moot. And that means they really had nothing to go on to prove any inherent suicidal tendencies.
Now, I'm not going to comment on whether the torture and solitary confinement for 8 months made him a little crazy. I'm sure it did. But the defense dept. obviously can't admit that they would be the catalyst for such behaviour, lol. No, they're basically saying that he was suicidal beforehand, and that's why they had to put him in solitary confinement in the first place (which is obviously
bull****).
That leaves the real reason.
Raison numeros dos. (I'm paraphrasing in French-Spanish for both our second-language compatriots). Which just so happened to take place only 1 week after the UN humanitarian torture expert started complaining.