Japanese prosecutors have begun an investigation into the leak of footage showing a collision between Chinese and Japanese ships near disputed islands that sparked a bitter diplomatic row.
The footage, shot in early September, was leaked to YouTube late last week.
It had previously only been shown to security personnel and some lawmakers for fear it could exacerbate the row.
On Tuesday, prosecutors seized records from Google to help identify the source of the leak, media reports said.
Google owns the YouTube video-sharing site.
The collision itself took place on 7 September near islands known as Senkaku in Japan and Diaoyu in China. The islands are controlled by Japan but claimed by China.
A Chinese trawler was seized after it hit two Japanese coast guard vessels near the islands, which have rich fishing grounds.
The incident triggered a political row that has yet to subside, with nationalist sentiment inflamed on both sides.
The Japanese government admitted on Monday that the footage posted on YouTube was authentic.
It shows the fishing vessel colliding with a Japanese coast guard ship, as its crew shout warnings for the ship to stop.
Officials say they do not know how the leak occurred.
"In order to quickly resolve the facts behind this incident, we filed a criminal complaint, because there are limits as to what we can achieve with an internal investigation," said coast guard chief Hisayasu Suzuki.
The footage has since been widely shown on Japanese television.
On Saturday, 3,000 people joined an anti-China demonstration in Tokyo to demand it abandon its claim to the islands. There have also been protests in China over the row.
The leak comes as Japan prepares to host the Asia-Pacific Economic Cooperation forum (Apec) summit in Yokohama on Saturday.
It is still not clear whether Chinese President Hu Jintao and Japanese Prime Minister Naoto Kan will hold a formal meeting there.