"It was a government plot to turn the public focus away from the verdict, which scrapped an appeal by the state to restore parliament's power to impeach the judges," he said.
Talking to a group of reporters at his office on Wednesday, the BNP leader said "the government often does something like this to divert attention on events that go against it".
"The abduction took place a day after the 16th amendment verdict was delivered. The aim was to divert the people's attention. This is our suspicion. We don't have anything to prove it," Fakhrul added.
His family alleged kidnap after he had called his wife to get the ransom money ready, while the BNP blamed it on the government.
After searches in the northwest region of the country, he was found on a Dhaka-bound bus in Jessore.
The police said there was no indication that Mazhar had been abducted.
Mirza Fakhrul termed the police claim 'humiliating'. "They don't understand that they are undermining their own image," he said.
The BNP leader also said even though he does not agree with Mazhar's political view, he respects the activist for his 'truthfulness, assiduity, sincerity and patriotism'.
"He is not only a poet and writer but also a scientist. Considering his thoughts about the environment, he is also a philosopher," Mirza Fakhrul said.
"You can't call him (Mazhar) a full communist if you read his writings, neither can you say he is a rightist. You can't even say he is fully a nationalist," said Fakhrul, who had embraced communist ideals in his student days.
"Are there many more people like him who understand Bangladesh in their own way? He wears lungi and panjabi made of khaddar. You will get an idea of his respect for all the religions if you visit his home."
"...He has never compromised," he added.