Galen explica sua motivação no filme em sua mensagem para Jyn:
When I was taken, I faced some bitter truths. I was told that, soon enough, Krennic would have you as well. As time went by, I knew that you were either dead or so well hidden that he would never find you. I knew if I refused to work, if I took my own life, it would only be a matter of time before Krennic realized he no longer needed me to complete the project. So I did the one thing that nobody expected: I lied. I learned to lie. I played the part of a beaten man resigned to the sanctuary of his work. I made myself indispensable, and all the while I laid the groundwork of my revenge. We call it the Death Star. There is no better name. And the day is coming soon when it will be unleashed. I've placed a weakness deep within the system. A flaw so small and powerful, they'll never find it.
Inicialmente, ele acreditava que eles poderiam conseguir sua filha. Então ele percebeu que não era realmente necessário, deixar de cooperar iria simplesmente atrasá-los, não pará-los. Então, mesmo que não conseguissem encontrar sua filha, ele continuou a trabalhar para eles para garantir que houvesse uma falha que os impedisse.
Edite com agradecimentos a Gallifreyan:
Aqui está a cena da história em quadrinhos, edição # 2
