N.H. Rev. Stat. § 106-B:12
Police employees shall be ex-officiis constables throughout the state. They shall have statewide authority to enforce all provisions of RSA title XXI relative to motor vehicle laws and the regulations relative to the transportation of hazardous materials, pursuant to RSA 106-A:18 and RSA 106-B:15. The director, division of state police, shall report to the director, division of motor vehicles, all violations of and prosecutions under the motor vehicle laws. Police employees shall have general power to enforce all criminal laws of the state and to serve criminal processes and make arrests, under proper warrants, in all counties. They shall not serve civil processes. No police employee shall act, be used or called upon for service within any town in any industrial dispute unless actual violence has occurred therein, and then only upon order of the governor. When any police employee shall apprehend any person who has committed or attempted to commit a felony the director shall immediately make a report to the attorney and the sheriff of the county and the chief of police of the municipality in which the offense was, or was suspected of being, committed and such cases shall be investigated and prosecuted by said county officials with the cooperation of said police employees. Further, police employees acting within 25 air miles of the international border with Canada, shall have the same authority and powers granted to forest rangers and officials of the division of forests and lands pursuant to RSA 227-G:7 and RSA 227-G:8.
RSA 106-B:12
1937, 134:13. RL 145:12. RSA 106:13. 1961, 166:4. 1967, 182:2. 1979, 344:4, eff. Aug. 21, 1979. 2017, 199 : 2 , eff. Sept. 3, 2017.