Section 18 — Territorial jurisdiction to inquire
Statutory text (Thai original)
ในจังหวัดอื่นนอกจากจังหวัดพระนครและจังหวัดธนบุรี พนักงานฝ่ายปกครองหรือตำรวจชั้นผู้ใหญ่ ปลัดอำเภอ และข้าราชการตำรวจซึ่งมียศตั้งแต่นายร้อยตำรวจตรีหรือเทียบเท่านายร้อยตำรวจตรีขึ้นไป มีอำนาจสอบสวนความผิดอาญาซึ่งได้เกิด หรืออ้าง หรือเชื่อว่าได้เกิดภายในเขตอำนาจของตน หรือผู้ต้องหามีที่อยู่ หรือถูกจับภายในเขตอำนาจของตนได้สำหรับในจังหวัดพระนครและจังหวัดธนบุรี
ให้ข้าราชการตำรวจซึ่งมียศตั้งแต่ชั้นนายร้อยตำรวจตรีหรือเทียบเท่านายร้อยตำรวจตรีขึ้นไป
มีอำนาจสอบสวนความผิดอาญาซึ่งได้เกิด หรืออ้าง
หรือเชื่อว่าได้เกิดภายในเขตอำนาจของตน หรือผู้ต้องหามีที่อยู่
หรือถูกจับภายในเขตอำนาจของตนได้ภายใต้บังคับแห่งบทบัญญัติในมาตรา ๑๙ มาตรา ๒๐ และมาตรา ๒๑ ความผิดอาญาได้เกิดในเขตอำนาจพนักงานสอบสวนคนใด
โดยปกติให้เป็นหน้าที่พนักงานสอบสวนผู้นั้นเป็นผู้รับผิดชอบในการสอบสวนผิดนั้น ๆ
เพื่อดำเนินคดี เว้นแต่เมื่อมีเหตุจำเป็นหรือเพื่อความสะดวก
จึงให้พนักงานสอบสวนแห่งท้องที่ที่ผู้ต้องหามีที่อยู่
หรือถูกจับเป็นผู้รับผิดชอบดำเนินการสอบสวนในเขตท้องที่ใดมีพนักงานสอบสวนหลายคน
การดำเนินการสอบสวนให้อยู่ในความรับผิดชอบของพนักงานสอบสวนผู้เป็นหัวหน้าในท้องที่นั้น
หรือผู้รักษาการแทน
English translation
In provinces other than Phra Nakhon Province and Thon Buri Province, senior administrative or police officials, assistant district officers, and police officials holding the rank of police sub-lieutenant, or a rank equivalent to police sub-lieutenant, and above shall have the power to conduct an inquiry into a criminal offense which has occurred, or is alleged or believed to have occurred, within their jurisdiction, or where the alleged offender has a residence in, or was arrested within, their jurisdiction. For Phra Nakhon Province and Thon Buri Province, police officials holding the rank of police sub-lieutenant, or a rank equivalent to police sub-lieutenant, and above shall have the power to conduct an inquiry into a criminal offense which has occurred, or is alleged or believed to have occurred, within their jurisdiction, or where the alleged offender has a residence in, or was arrested within, their jurisdiction. Subject to the provisions of Section 19, Section 20, and Section 21, where a criminal offense has occurred within the jurisdiction of any inquiry official, that inquiry official shall ordinarily be responsible for the inquiry into that offense for the purpose of prosecution, except where there is a necessity or for convenience, in which case the inquiry official of the locality where the alleged offender has a residence or was arrested shall be responsible for conducting the inquiry. In any locality where there are several inquiry officials, the conduct of the inquiry shall be under the responsibility of the inquiry official who is the head in that locality, or the person acting in that capacity.
This English translation is provided for reference only and has not yet been firm-verified — always rely on the Thai original.
Firm annotation
Section 18 is the core rule on territorial inquiry jurisdiction, and it distinguishes the historic Phra Nakhon and Thon Buri areas from other provinces by specifying which ranks may inquire. Jurisdiction attaches through any of several connecting factors: where the offense occurred, is alleged or believed to have occurred, or where the accused resides or was arrested. Read subject to Sections 19 to 21, its default rule is that the official of the place of the offense is the responsible inquiry official, unless necessity or convenience shifts responsibility to the place of residence or arrest. The final paragraph designates the head inquiry official, or the acting head, as responsible where a station has several officials, a point that decides who may lawfully conclude the file and forward an opinion to the prosecutor under Section 140.
Why this matters in practice
Territorial jurisdiction is a live defense: if the inquiry was run by an official with no jurisdiction under Section 18, the inquiry can be held unlawful, and an unlawful inquiry means the prosecutor has no power to prosecute under Section 120, which can end the case. Disputes often turn on exactly where the offense occurred or where the accused was arrested, so the underlying facts matter greatly. If you believe your case was investigated by the wrong station, a licensed Thai lawyer can test whether that defeats the prosecutor's authority to bring the charge.
Supreme Court decisions interpreting this section
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Supreme Court Judgment No. 1016/2567 (2024)
A dispute over whether the inquiry official was the head official in the locality under the final paragraph of Section 18, and thus the responsible official able to conclude the file under Section 140, is a factual question about who was the responsible inquiry official.
The defendant argued that the officer who filed the detention request was not the head inquiry official under the final paragraph of Section 18, so the inquiry was unlawful and the prosecutor had no power to prosecute. The Court characterized this as a factual dispute about which local official was the responsible one entitled to conclude the file under Section 140.
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Supreme Court Judgment No. 4313/2560 (2017)
Where the offense did not occur within the jurisdiction of the investigating station under Section 18 paragraph three, the inquiry is unlawful, and the prosecutor therefore has no power to prosecute under Section 120.
The Court found that the arrest actually took place at a different time and place, so the offense was not within the jurisdiction of the Laem Chabang police under Section 18 paragraph three. The inquiry was therefore unlawful and the prosecutor had no power to prosecute under Section 120, read with the Narcotics Case Procedure Act.
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Supreme Court Judgment No. 4732/2560 (2017)
Where an offense committed in the Kingdom is investigated by an appointed committee of inquiry officials, the head of that committee is the responsible inquiry official under Section 18.
For the charge committed within the Kingdom, the Court held the inquiry had to be run by the appointed investigation committee, whose head was the responsible inquiry official under Section 18, while the Attorney General acted as responsible official for related conduct falling under Section 140.
Curated decisions with case numbers verified against the Supreme Court database. English renderings are the firm's editorial translation for study.
Frequently asked questions
Which police station has the power to investigate a crime in Thailand?
Under Section 18, the inquiry official within whose jurisdiction the offense occurred, is alleged or believed to have occurred, or where the accused resides or was arrested. Normally the station where the offense happened is responsible.
What happens if the wrong police station investigates the case?
If the inquiry official had no territorial jurisdiction under Section 18, the inquiry can be held unlawful, and an unlawful inquiry means the prosecutor lacks the power to prosecute under Section 120.
Who is responsible when a station has several inquiry officials?
The final paragraph of Section 18 places responsibility on the inquiry official who is the head in that locality, or the person acting in that capacity.