The Gazette reports that Denver attorney Carrie Thompson says the detail could turn a jury against him, where in Colorado the jury could impose the death penalty.
Authorities say 22-year-old Marco Antonio Garcia-Bravo was charged with murder in the 2017 shooting of two high school students.
Prosecutors say if Garcia-Bravo is convicted, the defense could open the door to discussing his citizenship if his abusive childhood in Mexico is brought up.
The defense cites worries about how anti-immigrant rhetoric might influence the case.
The trial is scheduled for Jan. 6.
District Judge David Shakes holds the decision on what evidence is admissible.