The answer to this question is option 'C' - murder.

Explanation:
The intruder was already wanted for murder. This means that before the incident in question, the intruder had committed a murder and was being pursued by law enforcement authorities for that crime. The specific details of the murder are not provided in the question, so we can only infer that the intruder had taken another person's life unlawfully.

Reasoning:
There are several reasons why the correct answer is 'C' - murder. Let's explore them below:

1. Specificity of the question: The question asks what the intruder was already wanted for, meaning the intruder had a pre-existing criminal record. Out of the given options, murder is the most serious and heinous crime. Theft and robbery are property crimes, while kidnapping involves the unlawful taking or detention of a person. None of these options are as severe as murder.

2. Criminal hierarchy: In terms of severity, murder is considered one of the most serious crimes and is often categorized as a capital offense. It involves the intentional killing of another person, which is universally condemned and carries significant legal consequences. Theft, robbery, and kidnapping are also crimes, but they are generally considered to be of a lower magnitude compared to murder.

3. Law enforcement priority: Law enforcement agencies typically prioritize the apprehension of individuals wanted for murder due to the severity of the crime. Murder cases often receive more investigative resources, and the pursuit of suspects involved in such cases is usually more intense. This reflects the gravity of the offense and the need to bring the perpetrator to justice.

In conclusion, based on the given information and the reasoning provided, it can be determined that the intruder was already wanted for murder. This crime is the most serious out of the options given and carries significant legal implications.