Ansari was mercilessly beaten by a group of people last month and was allegedly forced to shout "Jai Sri Ram", after being suspected of involvement in a bike theft.
His two associates managed to escape from the spot and have not been traced so far by the police.
Ansari died in judicial custody a week after the thrashing incident. Eleven people have been arrested in connection with his killing.
The post-mortem report was submitted two days ago to the Seraikela police.
"During investigation it has been found that the officer-in-charge of two police stations did not react on time to save Tabrez Ansari. The local village head informed police about the incident at 2 a.m. but they reached the spot at 6 p.m.", a police source told IANS.
"The doctors attending Tabrez did not treat him well. The X-ray report indicated fracture in his head but he was not treated for brain haemorrhage. He was forwarded to jail," he said.
The Jharkhand High Court has sought a report from the state government regarding Ansari's killing.
The court has also sought a report on violent protests by members of the Muslim community on July 5 to protest the mob lynching of Ansari.
While the High Court has expressed unhappiness over the July 5 protests, no one has been arrested so far in this connection, despite police possessing CCTV footage.