The blast was initially believed to be an accident.
A DNA test confirmed that the key suspect, a man named Gao Wanfeng, died in the blast, police said.
Gao lived alone in Chaoyang Village, Shangyashan City, Heilongjiang Province, after three divorces.
He made a living by working in coal mines after he was released from prison in 2005.
He had disputes over injury compensation with a mine owner last year, state-run Xinhua said.
Forty people were injured in the blast, and they are being treated in the hospital.
