He wanted to make of Oliver as thief and all property let for himself. He went to the London to Fagin. Monks told everything to him. Nancy heard their dialog and told Rose about that. Fagin sent some guy to follow Nancy. He saw her speaking with Rose. Nancy betrayed Sikes and all gang. When Sikes heard it, he was shocked. He became mad. When Nancy returns, Sikes killed she. Then Sikes escape. Police found him and Sikes commit suicide. Fagin was executing. At the end Oliver was told truth about his family. His father had to marry an older woman and with her he had he son- Monks. But they were not happy together, so Oliver’s father found another woman. She was pregnant but Oliver’s father had to go to Italy, where he died. But he was quiet rich and he remained all his property to Oliver. That is why Monks wants Oliver to be a thief and paid for it.