Modi has faced criticism for not speaking strongly enough against Hindu vigilantes targeting Muslims and other minorities, but called Wednesday for strong action against those guilty of the brutal attack.
“The lynching in Jharkhand has pained me. Everyone… is grieved at the loss of life of the youth, and the guilty should be given harsh punishment,” he said in the upper house of parliament.
Police in Jharkhand have so far arrested 11 men in connection with the attack — including the main accused, who was seen thrashing Tabrez Ansari in a video that went viral on social media.
Ansari, 24, had been accused by villagers of burglary. He was tied to a pole and beaten for up to 12 hours before police first detained him.
They took him to hospital, where he died Saturday. Indian opposition parties accuse Modi of not doing enough to stop communal attacks that have increased since his nationalist Hindu Bharatiya Janata Party took power in 2014.
The party was re-elected with a resounding majority last month.
Modi said also he was saddened by the deaths from Acute Encephalitis Syndrome of over 150 children in eastern Bihar state.
“We have pressed resources to fight the encephalitis epidemic and we have to fight this together,” he said of the virus, which scientists say could be spread from a toxin found in ripening lychee fruit.