Three people were detained in connection with the killing of Sister Valsha John, the police said on Friday.
"We have detained three people on the suspicion of their complicity. We have sent a police team to search for another five persons," Arun Oraon IG, Police (Santhal Parganas) told PTI.
Oraon, however, said that the detainees' names would not be disclosed unless they were arrested.
The police, who filed an FIR against unknown persons, was inquiring into the killing of 52-year-old Sister Valsha John at Pachwara village in Jharkhand's Pakur district on Tuesday night.
A resident of Kerala's Ernakulam district, she had been staying at Pachwara village for several years and spearheaded an anti-displacement movement against Panem Coal Mining Company in Pakur's Amrapara block.