You know, they are mostly Khazars, not Judeans.
This is the genetic evidence. For the historical evidence, read "The Thirteenth Tribe".
If you want the actual people mentioned in the Torah (which today's "Jews" have almost nothing to do with), look to the actual descendents of Jacob/Israel, i.e. those who are carrying the Y chromosome of the Cohannim/Levites, who have maintained enough of a genetic signal through faithful paternal lineage as officers of the temple to prove their actual heritage as the chosen (unlike the Khazar impostors.)