Chief Justice Saqib Nisar on Wednesday said there was a "campaign" behind the murder of Mashal Khan, a 23-year-old university student who was lynched by a mob on accusations of blasphemy last month.

"The news of the lynching did not even reach the police," the chief justice said.

He was chairing a three-member bench of the apex court conducting a suo motu hearing of the incident that occurred on the premises of Abdul Wali Khan University in April.

Mashal was attacked by a vigilante mob, incited by rumours, for allegedly "publishing blasphemous content online". The mass communication student was beaten and shot by the mob and succumbed to the injuries he received.

The Supreme Court had taken up suo motu notice of the harrowing incident and directed police to regularly provide details of the incident to it.

During Wednesday's hearing, Nisar asked whether video footage of the incident, that showed the mob of university students kicking the lifeless body of the victim and beating it with wooden planks, had been obtained via CCTV footage or social media.

"We know what happened to the body of the victim," he said.

Lawyer Khawaja Izhar told the apex bench that the video was enough to serve as evidence in the case.

Izhar also told the court that Mashal's sisters have been unable to continue their education since the incident.

Khyber Pakhtunkhwa police presented a report before the apex court, detailing the number of arrests made so far in the case.

"Fifty-three suspects have been arrested," the report said. "Of those, 49 are in jail and four have been sent on remand while two others have escaped."

"The key suspect in the case, Imran, has been arrested. He has accepted his crime," the report added.

"Have the arrested suspects been convicted?" the chief justice asked.

Iqbal Jan, the father of Mashal Khan, present in the court, told the bench that the police had so far arrested "actors", and not the "directors" behind the brutal lynching of his son.

"My son was beaten from 10am till 3pm," Jan told the apex bench.

"Police was present during the [lynching] but did not take action," he added. "My son was an asset of the country."

The chief justice said that the if the police had been negligent during the incident, a thorough investigation will be conducted.

The hearing was adjourned for three weeks.