Redeeming a Heretic:[1]

A Jewish captive who became a heretic is prohibited from being redeemed from captivity. A person is considered a heretic if he transgresses even a single command [even one time[2]] with the purpose of rebelling against G-d [i.e. להכעיס], such as if he eats non-kosher meat even when he has ability to eat kosher meat [for the same price and effort].[3]

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[1] Michaber 251:2; Rama 252:6; See Maharam Milublin 15; Kneses Yechezkal Y.D. 38; See Chasam Sofer Bava Basra 8a; Chidushei Chasam Sofer Shabbos 22a; Drashos 1:141; Toras Moshe Parshas Mikeitz; Parshas Beshalach that it is specifically observant Jews who have such suffering during captivity

[2] Shach 251:3; Taz 251:1

[3] No intention to rebel but transgresses due to lack of belief in the command: If the transgressor did not perform the transgression out of rebellion but rather simply out of lack of care/belief in the command then although there is no obligation to support him, nevertheless it is not forbidden to do so. [Implication of Shach 251:3, See Admur Hilchos Shechitah 2 who differentiates with regards to being allowed to shecht between one who just doesn’t believe/care about the command and one who has intention to rebel.]    

No intention to rebel and transgresses simply out of lust and leisure: If a person transgresses for reasons of leisure, then although there is no obligation to redeem him, nevertheless, there is no prohibition to do so. [Rama 251:2]