After immigrants are detained by ICE, there are probably records somewhere of who has an attorney, and who is calling family members or an attorney.
For the immigrants who aren’t calling any family or lawyers, the poorest of the poor, people with little to no connection to anyone, who may not even say which country they are from, if the administration were actually trying to kill as many disconnected immigrants as possible in secret, would society know?
For example, if the administration was composed of all types of conservative people, but 30 percent were secretly Nazis or wanted racial genocide, could there be a campaign to not just remove, but kill, immigrants, and the public doesn’t find out?
At what point you consider the exterminations “mass” is somewhat arbitrary. Slave population has remained relatively steady (highest per capita in the world, but steady) while the rate at which we eliminate “undesirables” is shooting up in a way that’s really difficult to track or hold anyone accountable for