Imam Maulana Habib Ur Rehman of the Glasgow Central Mosque - the largest in Scotland - supported killer Mumtaz Qadri in a series of WhatsApp messages, the BBC reported today.
Qadri, a former police commando, was hanged on February 29 after he gunned down Punjab governor Salman Taseer, who opposed Pakistan's controversial blasphemy laws.
Qadri was working as a bodyguard for Taseer when he pulled out a gun and shot him 28 times in 2011 in broad daylight in an upmarket locality of Islamabad.
The imam's messages, seen by the BBC, detail how he was "disturbed" to hear of his death and gave him the religious blessing usually reserved for devout Muslims.
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The imam said he was "disturbed" and "upset" before he wrote the messages, seeking God's mercy be upon Qadri.
In another message, he wrote: "I cannot hide my pain today. A true Muslim was punished for doing which [sic] the collective will of the nation failed to carry out."
He told the BBC: "The assassination of Salman Taseer is widely condemned.
"Whether I agree or disagree with the views he expressed, as an Imam and as a human being I express abhorrence at the manner in which he was executed.
"The execution was not in accordance with Islamic teachings and principles."
He said: "Mumtaz Qadri's execution is condemned as it is not in accordance with due process nor is it in accordance with Islamic teachings and principles.
Reacting to the imam's remarks, lawyer and activist Aamer Anwar accused the religous leader, who condemned the Brussels bombings, of "rank hypocrisy".
He told BBC Scotland many people within the community were scared the views would "filter down the Muslim community and radicalise our children".