China is reeling after yet another in a series of deadly attacks on schoolchildren. On Wednesday, an assailant with a meat cleaver brutally murdered seven children and two adults at a private kindergarten in the inland city Hanzhong. It was the fifth such attack since March. Following, an instant guide to this disturbing trend:

In total, how many children have been killed or injured?
The seven who died today are the first children to die since March, when eight elementary school students were killed and five injured by a knife-wielding attacker in Fujian province. In three intervening attacks in April and May, there were no reported fatalities but dozens of children were injured: Five by a hammer-wielding farmer in the eastern Chinese city of Weifang on Friday; as many as 29 four- and five-year olds by a man with a knife in Jiangsu province; and 15 elementary schoolers in the southern Guangdong province, also by a man with a knife.

Who are the attackers?
Today's killer, 48-year-old Wu Huanming, owned the school property and had argued with an administrator, who was among the victims, according to reports. The Weifang attacker was reportedly a farmer angered by a government order to demolish his newly built house. The Jiangsu attacker was a 46-year-old unemployed man, and the assailant in Guangdong was a 33-year-old former teacher with mental health problems. The March incident was perpetrated by a former community doctor, who was executed in late April for the crime.

Are the attacks linked?
They don't appear to be. According to the Associated Press, the attacks are more likely to be "copycat actions."

Why did they happen?
No-one knows exactly, though plenty of people are speculating. Chinese sociologists suggest to the BBC it is "social revenge," carried out by people with "grudges against society" who "try to take revenge by attacking the young and vulnerable." In China, there is a belief "that the attacks underscore the absence of adequate pressure-release valves in a society that is going through rapid economic upheaval," says Edward Wong in The New York Times. Moreover, a very few of the estimated 173 million Chinese suffering from mental illness have ever received treatment.

What are the Chinese authorities doing about the disturbing trend?
The Ministry of Public Security had previously ordered increased police patrols at schools. The government has also been censoring coverage of the attack, "perhaps to prevent other copycat murders, or perhaps to play down any suggestion of dysfunction within Chinese society," reports The New York Times.

Sources: BBC, Associated Press (2), The New York Times (2), Xinhua, Reuters

This article originally ran on May 4.