A CHRI delegation visited the violence-affected Shabbirpur and neighbouring villages in the district, as part of a national level fact-finding team led by the National Campaign on Dalit Human Rights (NCDHR).
"Together with the team, the CHRI strongly condemns the mass attack on Dalits in Shabbirpur village on May 5 and the failure of the local administration in preventing and stopping the violence," it said in a statement.
At the minimum, the inquiry must include a review of the steps taken by the state police to monitor law and order in the district following unrest in April, it said.
The CHRI said it must also include "steps taken by all concerned police units in charge of the affected villages to ascertain legality and necessity of all their actions including assessing threat levels, requesting additional force, and actions to stop the violence; and allegations claiming delay in registering FIR for the Dalit victims and ill-treatment by the police personnel".
About a dozen police vehicles were set ablaze and 12 policemen were injured on May 9. On May 23, another person was shot dead and two others were wounded.