A suicidal man is reported to have started a fire on a packed commuter bus in south-eastern China that killed 47 people.
State media said a suicide note was found at his home in the port city of Xiamen, where the attack place.
The suspect, named as Chen Shuizong, aged about 60, was among those killed.
Police began a criminal investigation after traces of petrol were found on the diesel-powered bus and the fuel tank survived intact.
More than 30 people were injured in the fire during the evening rush hour on Friday.
Xinhua news agency quoted a government statement that said Chen Shuizong carried out the attack because he was unhappy with life and wanted to vent his anger.
The statement added that DNA evidence identified him as the key suspect.
Officials closed the entire express bus system after the incident. Public Security Minister Guo Shengkun was sent to oversee the investigation.
A BBC correspondent in Shanghai said there have been a number of such incidents on buses in recent years by people with personal and sometimes political grievances.
In 2009, an unemployed man ignited petrol on a bus, killing himself and 26 others. Another 24 people died the same year in a shuttle bus fire started by a disgruntled steel worker.