URGENT: 單身老貓-

Hi 單身老貓-
My nephew was charged with assulting female (slapping his girlfriend with blodding) and he is in the jail. He could have pre-trial release but the immigration office has held it, and told us he may have chance to be deported. Do we need to hire an immigration lawyer to deal with it if he was convicted and deported? Why the immigration officer can decide the deporting without waiting till his guilty is confirmed by the criminal court??

Thanks!!!