Which action is illegal under the definition of burglary in Missouri?

The action that is classified as illegal under the definition of burglary in Missouri is unlawfully entering a structure to commit theft. Burglary, as defined in Missouri law, involves entering a building or structure without permission and with the intent to commit a crime therein, which often includes theft. The essence of burglary lies in the intent to commit a crime while unlawfully entering or remaining in a property.

This definition highlights the importance of both the unlawful entry and the intent to commit a crime at the time of entry, making this option a clear violation of the law. In contrast, simply entering a house with the intent to sleep does not constitute burglary unless there is intent to commit a crime. Remaining unlawfully without intent to commit a crime does not satisfy the requirements for burglary, nor does leaving a property without taking anything, as there is no unlawful intent or action that fits the criteria of burglary in these scenarios.