The man in the tree / Sage Walker.

"A Tom Doherty Associates Book" -- From title page.

"Humanity's last hope of survival lies in space... but will a random death doom the venture? Our planet is dying and the world's remaining nations have pooled their resources to build a seed ship that will carry colonists on a multi-generational journey to a distant planet. Everything is set for a bright adventure... and then someone is found hanging dead just weeks before the launch. Fear and paranoia spread as the death begins to look more and more like a murder. The authorities want the case settled quickly and quietly so as not to cause panic... and to prevent a murderer from sabotaging the entire mission."--Amazon.com.