Why was Gervasio unable to see his son in the novel, Where the Air Is Clear?

Gervasio is Rodrigo's father but they have never met. At the time of his wife's pregnancy, Gervasio was in the Belen war prison; he escaped with three other prisoners. In their search for a Zapata camp they could join, the fugitives separated; Gervasio was caught first and told his captors where to find his friends, because he didn't want to die alone.