But on Wednesday, the latest in a streak of copycat assaults was also the most deadly: a landlord with a kitchen cleaver barged into a kindergarten in central China, hacked to death seven children, their teacher and her mother and returned home while rescuers rushed to the scene before taking his own life.

What prompted the attack — the fifth assault on schoolchildren since March — was as imponderable to many Chinese as the details were gruesome. They have all involved middle-aged men in small towns expressing violent grievances against the most vulnerable and cherished members of their communities, the children of families often limited to having only one.

But whether the problem is weak diagnosis and treatment of mental illness, lackluster security and little money for schools, too much media attention to spectacular crimes or too little public debate about social inequality, the killings have presented an unusual political and security challenge to the ruling Communist Party.