"We have detained three people on the suspicion of their complicity. We have sent a police team to search for another five persons," said Arun Oraon IG, Police (Santhal Parganas).
Oraon told the media that the detainees' names would not be disclosed unless they were arrested.
Police have filed an FIR against the accused and is enquiring into the case. The incident took place at the Pachwara village of Jharkhand's Pakur district.
Valsha, a resident of Pachwara village, had been spearheading an anti-displacement movement against Panem Coal Mining Company in Pakur.