Mo. Rev. Stat. § 565.225: Stalking, first degree, penalty.

1. A person commits the offense of stalking in the first degree if he or she knowingly, through a course of conduct that is directed at another person or through technological abuse conduct, engages in conduct that would cause a reasonable person under similar circumstances to:

(1) Fear death or bodily injury to the person;

(2) Fear that an offense will be committed against a member of the person's family or household members, or an individual with whom the person has a dating relationship;

(3) Fear that an offense will be committed against the person's property; or

(4) Feel harassed, terrified, or intimidated.

2. Any law enforcement officer may arrest, without a warrant, any person he or she has probable cause to believe has violated the provisions of this section.

3. This section shall not apply to activities of federal, state, county, or municipal law enforcement officers conducting investigations of any violation of federal, state, county, or municipal law.

4. The offense of stalking in the first degree is a class E felony, unless the defendant has previously been found guilty of a violation of this section or section 565.227, or any offense committed in another jurisdiction which, if committed in this state, would be chargeable or indictable as a violation of any offense listed in this section or section 565.227, or unless the victim is intentionally targeted as a law enforcement officer, as defined in section 556.061, or the victim is targeted because he or she is a relative within the second degree of consanguinity or affinity to a law enforcement officer, in which case stalking in the first degree is a class D felony.