They came in the dead of night; no one saw them and nobody knew they were there. Moments later, the Japanese ninja museum was missing a safe full of cash.
Under cover of darkness, thieves vanished with the 150-kilogramme (330-pound) strongbox containing around $9,500, paid as admission fees to the Iga-ryu Ninja Museum in central Japan.
The museum is dedicated to the legend of the ninja -- the covert martial arts masters and agents of sabotage who prowled the shadows in feudal times, and were famous for secrecy and stealth.
But police called to investigate the crime found that the culprits had been less than subtle -- having forced their way into the museum office with a crowbar, Kyodo News agency reported.
The safe, which was stolen in the early hours of Monday, contained takings from around 1,100 weekend visitors, the Asahi Shimbun daily reported.
The museum, in Iga, features a traditional ninja house and offers interactive experiences, allowing visitors to learn about ninja skills, throw star-shaped weapons, and watch ninja shows.
Iga, which is 350 kilometres (220 miles) southwest of Tokyo, is home to one of the two most famous ninja clans.
The city's Mie University set up the world's first research centre devoted to ninja in 2017, and opened a graduate course a year later.