( CNN ) Igniting a live man in a cage ; severing the heads of dozens ; kidnapping , raping and selling women and children -- ISIS ' shocking maltreatment of its captives has become regrettably predictable . But that has made their latest decision on the fate of 19 Christian prisoners all the more surprising to some . On Sunday , ISIS released them . Ten other Assyrian Christians are expected to join them in freedom after a short time in captivity . All but one of the Christians released were part of a group of 220 Assyrians captured last week during offensives on northern Syrian villages , said the London-based Syrian Observatory for Human Rights . In the shadow of its sadistic mercilessness , the sudden reversal leaves many asking : Why ? The group has not explained its decision . Here are some possible answers . It was not a militant commander but an ISIS Sharia judge , said Osama Edward , who heads the Assyrian Human Rights Network , based in Sweden . Some of Edward 's family members are among the captured Christians . His rights group keeps contact with local people , via phone and Internet , and has a field team in Syria , he said . The Sharia judge asked the Christians if they were part of any militia , Edward said . Then he pronounced them not guilty of violating Sharia law and ordered them released . The Assyrian Christians were all from the village of Tal Goran . They have returned home but are keeping quiet for now . Can Christianity survive in the Middle East ? `` They were so tired , '' Edward said . They had a closed meeting with a bishop , and then ate and went home . `` They were treated well , '' contacts in Tal Goran passed on to Edward . `` Nobody was tortured . '' Not to Graeme Wood , who published a detailed analysis on ISIS ' religious inner workings this week in The Atlantic . He was pleased to hear about it , but he felt it fit into ISIS ' plans . `` ISIS has claimed for a long time to follow rules , and it claims that these Sharia courts will impose limits , '' he told CNN . `` They can attempt to get credibility by showing that they follow rules and that they have some kind of transparent process that follows their particular implementation of Sharia law . '' It 's possible . It did win them points with Assyrian activists . `` It 's a good sign to show that 'we can talk , ' '' Edward said . ISIS has taken heat even from other Islamists who accuse it of rogue justice , especially against Muslim civilians they 've condemned as `` infidels '' out of hand . It 's part of the reason al Qaeda has rejected the group , Wood wrote . That reduced some of ISIS ' chances of receiving international moral and financial support , leaving the terror group to make up the gap with other funding . And it has led to a violent split with another jihadi group in Syria , the al-Nusra Front , according to The Washington Institute for Near East Policy . Other Islamist groups in Syria have frowned on ISIS for not submitting to decisions from Sharia courts . The main issue drawing anger from other Islamist groups revolves around Muslim civilians , who are ISIS ' most common victims . And the released captives are Christians . But Christian activist Edward thinks the ISIS Sharia court decision was , in part , a nod to Syrian Sunni Muslim tribal leaders who negotiated for the Christians ' release . First , the tribes care deeply about their Christian neighbors and do n't want them killed , Edward said . It also makes the Sunni tribal leaders look good and gets a rapport started between them and ISIS . ISIS has a very narrow definition of who is a real Muslim and who is an apostate . Foremost , a Muslim must practice Sunni Islam in its eyes . The group is quick to practice `` takfir , '' which amounts to the excommunication of a Muslim , for things as seemingly petty as shaving off one 's beard or voting in an election . ISIS is quick to kill anyone it condemns , because it wants to create a fanatically pure caliphate with only the strictest devotees , Wood wrote . ISIS has executed 125 of its own members for doing things that broke with its strict take on Islam , the Syrian Observatory said . Yes . Even in the strictest interpretation of Islam , there is a provision for sparing Christians , Wood wrote . Social media posts indicate that ISIS carries out mass killings regularly , but `` exempted from automatic execution , it appears , are Christians who do not resist their new government . '' They are required to pay a special tax and acknowledge the new ruling power . That 's exactly what the judge ruled , Edward said . The released Assyrian Christians agreed to acknowledge ISIS as their new masters and to pay the tax . ISIS is still holding two of Tal Goran 's Christian villagers , Edward said . They should be released as soon as the taxes are paid . He is hoping for the same deal for the other Christian villagers , including for his family . CNN 's Samira Said and Dana Ford contributed to this report .
ISIS released 10 Assyrian albums on vinyl and plans to release two more . The sudden reversal has puzzled many .