כִּי־יִמָּצֵ֣א אִ֗ישׁ גֹּנֵ֨ב נֶ֤פֶשׁ מֵאֶחָיו֙ מִבְּנֵ֣י יִשְׂרָאֵ֔ל וְהִתְעַמֶּר־בּ֖וֹ וּמְכָר֑וֹ וּמֵת֙ הַגַּנָּ֣ב הַה֔וּא וּבִֽעַרְתָּ֥ הָרָ֖ע מִקִּרְבֶּֽךָ׃
The Five Books of Moses, by Everett Fox
The capital crime here would appear to be the sale of specifically an Israelite as a slave.