There are no laws in Oceania. As Winston Smith understands, as the novel opens, "nothing was illegal, since there were no longer any laws."
Nevertheless, Winston Smith commits crimes. He knows from the moment he opens his journal that even thinking of keeping a private diary is a thought crime. It is a crime because it never should occur to him, as an orthodox Party member, to act in such a way. A thought crime, he knows, is punishable by death—or, at the very least, twenty-five years in a forced labor camp.
Winston, however, goes past mere thought crimes, actually conspiring against the state. He and Julia are lured by O'Brien into what they think is a group of conspirators who are plotting rebellion. They are caught on tape saying they would like to overthrow the government and telling O'Brien that they are willing to commit the following crimes to do so:
"You are prepared to cheat, to forge, to blackmail, to corrupt the minds of children, to distribute habit-forming drugs, to encourage prostitution, to disseminate venereal diseases—to do anything which is likely to cause demoralization and weaken the power of the Party?"
"If, for example, it would somehow serve our interests to throw sulphuric acid in a child’s face—are you prepared to do that?"
Winston, of course, is not charged with anything specific when he is arrested and brought to the Ministry of Love, but he has obviously stepped over many lines in his desire to rebel against the Party and its totalitarian worldview.