Nagao is best known for his photograph of Otoya Yamaguchi assassinating Japanese Socialist Party politician Inejiro Asanuma.

At the time Nagao was a cameraman working for Mainichi Shimbun.

[1] Nagao won the 1960 World Press Photo of the Year award and the 1961 Pulitzer Prize.

The first award allowed Nagao to travel abroad widely, impossible for most Japanese people at the time.

[2] Nagao left the newspaper in 1962 and became a freelance photographer.