A man belonging to the minority Ahmadi community, Tahir Ahmad, who was on trial for blasphemy, was shot dead in a courtroom in Peshawar on Wednesday.
The young assailant, identified as Khalid Khan, managed to get into the court amid tight security. He was later arrested.
Ahmadis, a four million-strong minority group in Pakistan, have faced death, threats, intimidation and a sustained hate campaign for decades.
The incident is widely condemned by human rights orgzations. In a tweet, Amnesty International said, "The murder of Tahir Ahmad, who is reported to have a mental disability, in the Peshawar Sessions Court this morning is yet another example of how Pakistan's blasphemy laws embolden vigilantes to threaten or kill the accused".
Prof. M Ismail from Peshawar tweeted, "Pakistan has become a hell, the society has become extremely intolerant. This guy was killed by a man inside the court in Peshawar today. He was charged in a blasphemy case. The killer said the Prophet PBUH ordered him in a dream to kill this guy because he was Ahmadi (Qadiane)."
Ahmadis insist they follow Islam. However, Pakistan declared the group non-Muslim in 1974 for regarding their sect's founder, Ghulam Ahmad, as a prophet. Orthodox Islam holds there can be no prophets after Muhammad.
Nasim was arrested two years ago on blasphemy charges after claiming he was Islam's prophet.
Pakistan's controversial blasphemy law carries an automatic death penalty for anyone convicted of insulting God, Islam, or other religious figures.
Many members of the minority communities in Pakistan - the Ahmadis, Hindus, Christians and Sikhs were charged with draconian blasphemy law. Many of them are languishing in jails on the false charges of disrespecting the Quran.
( With inputs from ANI )