"We did not find any concrete evidence under which an investigation or legal action can be launched against Mashal, Abdullah or Zubair," Inspector General of Police Salahuddin Khan Mehsud told reporters at a press conference here.
Mashal, a journalism student at the Khan Abdul Wali Khan University in Mardan in Khyber-Pakhtunkhwa, was stripped, beaten and shot in the head and chest by the mob on Thursday.
Mehsud said that prior to the murder, investigating officers had not found anything on social media but after the incident, there was a lot of activity.
He added that police have sought the help of Federal Investigative Agency (FIA) because there are manufactured, edited pictures and videos on social media sites for which we need an expert opinion of the FIA.
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"I will ensure that the investigation is impartial," he said.
"Details of the incident will be submitted to the Supreme Court tomorrow. It will contain all major and minute details of our investigation," the IGP said.
A local imam had refused to lead Khan's funeral prayers on Friday. A technician led the funeral prayer.
University officials had issued a public notification hours before Khan's murder naming three students being investigated for "blasphemous activities".
Prime Minister Nawaz Sharif last week issued a strongly- worded condemnation of the lynching of the student, saying the entire nation should be united in condemning this crime and to promote tolerance and rule of law in the society.
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