criminal investigation; investigative net
Refers to the scope or network of a criminal investigation, often used in police or detective contexts. Can imply the investigative reach or the line of inquiry.
警察は広範囲に捜査線を張った。
The police cast a wide investigative net.
新たな証拠が見つかり、捜査線が拡大された。
New evidence was found and the investigation was expanded.
Compound of 捜査 (investigation) and 線 (line, network). The exact historical derivation is uncertain, but the term is conventionally associated with the idea of an investigative perimeter or line of inquiry.