為虎作倀

I think you are looking for the phrase "为虎作伥", Chinese Pinyin: "Wei Hu Zuo Chang" and the explanation on the book is correct. Usually we use this to describe someone who is the victim and has all the reason to resent those bad guys, but instead work for them to hurt more people.

为虎作伥（wèi hǔ zuò chāng）：比喻帮助恶人作恶，帮坏人干坏事，帮凶。出自 《太平广记》。 伥：伥鬼。旧时迷信，认为被老虎咬死的人，他的鬼魂又帮助老虎伤人，称为伥鬼。比喻帮助恶人作恶，帮坏人干坏事，帮凶。 (见百度)

为虎作伥(wei hu zuo chang) There is a story told that people eaten by tiger wei changes into the"伥”(a kind of ghost),the “伥”will help the tiger to hurt more people. Now It means the peolpe who helps the bad person to do some bad things. You can search it on baidupedia(www.baidu.com)

为虎作伥 [wèi hǔ zuò chāng] 1. play the jackal to the tiger; abet one's enemy; act as the paws of the tiger; assist the evildoer; hold a candle to the devil; help an evil man (do evil); help a villain do evil; help the tiger to pounce on [upon] its victims: The local bully's henchmen were his agents in oppressing the people. 土豪劣绅的狗腿子为虎作伥， 欺压百姓。 旧时迷信，以为被虎吃掉的人，死后会成为伥鬼，虎出行求食，伥鬼为虎前导清道。后以“为虎作伥”比喻做恶人的帮凶。 邹韬奋《我们的灯塔》：“我们因谈起民族解放的重要，连带想到阻挡这个解放斗争的帝国主义。但同时不要忘却为虎作伥的封建残余的势力。”