At least two people were killed and another 21 injured in a knife attack in a hospital in China’s southwestern province of Yunnan on Tuesday, local authorities said.

The attack took place just before midday at Chengnan Hospital in Zhenxiong, the county’s public security bureau said in a statement.

A 40-year-old man was arrested and the case is under investigation, local police said.

Authorities said they do not know the motive for the attack.

The alleged attacker’s cousin said he had previously been jailed for three years for injuring others in a dispute over a motorcycle transaction, according to the state-owned Henan Daily.

“Before he was imprisoned, his character was still good. He used to behave well. But after he came out…he felt that he had been wronged,” the cousin was quoted as saying.

The report has since been deleted from Chinese news platforms, where censors routinely scrub content.

Another report from the Cover News, a state-owned media outlet, confirmed the suspect was sentenced to three years in jail for “intentional injury” in 2013, citing a court document.

China, where private gun ownership is illegal is for most civilians, has faced a spate of mass stabbings in public places in recent years.