Oh I see so he thought Polaris or Hedron was the threat. Seems The Hiss were playing him really good in thinking they had good intentions for the beginning. But I remember that Trench got more and mire crazy, hence the reason he killed him self, because the hiss found him unworthy in the long run. I hope we will see Darling again too.
This was revealed when during the Office Nightmare sequence if you let Trench mumble to himself at the second attempt he rants about how everyone has betrayed him by siding with Hedron (and using the HRAs) and how bringing in the Hiss is the only solution.
This puts a spin on all those documents we found about Trench becoming more irritated and all the hotline calls of him being more paranoid.
I don't think it was outright stated how Trench was killed, but I suspected it's because the Service Weapon, and the Board, finally deemed him unworthy or compromised and had him 'fired'.