Kumar also spoke with his Haryana counterpart Manohar Lal Khattar, requesting him to meet the family members who hail from Bihar's Madhubani district.
In his telephonic conversation, Kumar said a meeting of the Haryana chief minister with the deceased's family would not only instill a sense of confidence but also ensure a faster and impartial probe, an official release said.
Khattar assured Kumar that he would meet the family members, it said.
Kumar had yesterday also asked Khattar to take stern action against those involved in the killing.
On the chief minister's directive, Bihar Director General of Police P K Thakur had talked to his Haryana counterpart and requested him to to take the strongest possible action against the culprits.
The class 2 student was found dead with his throat slit inside a toilet of Ryan International School on September 8.