The Afghan interior ministry says its officials are questioning two men in connection with the fatal shooting of Japanese doctor and aid worker Tetsu Nakamura.
The ministry told NHK it believes the two men may know something about the incident.
Nakamura was shot and killed last Wednesday in Jalalabad in the eastern province of Nangarhar while he and his staff were travelling in two cars. Five others were also killed.
Nakamura was the local representative of Japanese nongovernmental organization Peshawar-kai.
Investigators have found that an armed group in a white car waited for Nakamura's vehicle, blocked its way and then opened fire.
Security camera footage shows the suspected gunmen getting onto two white cars and driving away.
Nakamura worked to improve living standards in Afghanistan for decades through irrigation system construction and other contributions.
Afghan officials and local residents have praised his contributions.