Thank you for the additional information. Yes, he could be charged with a violation of your privacy, which is criminal and I have provided the law below, for you to review and to apply to the facts. You can go to the police and file a report and allow them to investigate. They can appear and try and resolve this and speak with him, seeing if he will agree to remove them or else could be arrested and charged. Now, if this turns civil, then you would need to proceed through the court and get a court order, which would require him to remove them as well. Since your attempts with the letter have not provided any results, the police can be called and/or a civil action for the invasion will need to be filed.
644:9 Violation of Privacy. –
I. A person is guilty of a class A misdemeanor if such person unlawfully and without the consent of the persons entitled to privacy therein, installs or uses:
(a) Any device for the purpose of observing, photographing, recording, amplifying, broadcasting, or in any way transmitting images or sounds of the private body parts of a person including the genitalia, buttocks, or female breasts, or a person's body underneath that person's clothing; or
(b) In any private place, any device for the purpose of observing, photographing, recording, amplifying or broadcasting, or in any way transmitting images or sounds in such place; or
(c) Outside a private place, any device for the purpose of hearing, recording, amplifying, broadcasting, observing, or in any way transmitting images, location, movement, or sounds originating in such place which would not ordinarily be audible, visible, or comprehensible outside such place.
II. As used in this section, "private place'' means a place where one may reasonably expect to be safe from surveillance including public restrooms, locker rooms, the interior of one's dwelling place, or any place where a person's private body parts including genitalia, buttocks, or female breasts may be exposed.
III. A person is guilty of a class A misdemeanor if that person knowingly disseminates or causes the dissemination of any photograph or video recording of himself or herself engaging in sexual activity with another person without the express consent of the other person or persons who appear in the photograph or videotape. In this paragraph, "disseminate'' and "sexual activity'' shall have the same meaning as in RSA 649-A:2.
III-a. A person is guilty of a misdemeanor if, for the purpose of arousing or gratifying the person's sexual desire, he or she knowingly views another person, without that person's knowledge or consent, in a place where one would have a reasonable expectation of privacy. For purposes of this paragraph, "views'' means looking at another person with the unaided eye or any device intended to improve visual acuity.
IV. A person is guilty of a misdemeanor if such person knowingly enters any residential curtilage, as defined in RSA 627:9, I, or any other private place as defined in paragraph II of this section, without lawful authority and looks into the residential structure thereon or other private place with no legitimate purpose.
V. Paragraphs I and II shall not be construed to impair or limit any otherwise lawful activities of law enforcement personnel, nor are paragraphs I and II intended to limit employees of governmental agencies or other entities, public or private, who, in the course and scope of their employment and supported by articulable suspicion, attempt to capture any type of visual image, sound recording, or other physical impression of a person during an investigation, surveillance, or monitoring of conduct to obtain evidence of suspected illegal activity, the suspected violation of any administrative rule or regulation, a suspected fraudulent insurance claim, or any other suspected fraudulent conduct or activity involving a violation of law, or pattern of business practices adversely affecting the public health or safety.