Thousands of schools collapsed during the quake last May
Chinese police have arrested a man who was investigating whether poor construction caused schools to collapse during last year's massive earthquake.
The detention of Tan Zuoren is part of a crackdown in Sichuan province just weeks ahead of the first anniversary of the quake, a human rights group said.
The magnitude-8.0 earthquake left about 88,000 people dead or missing, and five million homeless.
Officials have never released a figure for the number of children who died.
Tan Zuoren had asked internet users and people who lost their children in the quake to help to compile a detailed database of the victims.
He also asked volunteers to detail any evidence of poor construction at the schools.
Mr Tan was detained on 28 March on charges of subversion of state policies, according to the Centre for Human Rights and Democracy.
Several thousand school buildings collapsed during the earthquake, fuelling angry allegations by parents that corruption had led to shoddy construction standards.
In many of the affected towns, schools collapsed but other nearby buildings withstood the earthquake.
Government officials promised an investigation while, at the same time, pressurising parents to keep their grief - and their anger - to themselves.
Mr Tan was the latest of several government critics to be detained or summoned for questioning in recent weeks, the Centre for Human Rights and Democracy said.