BNP Secretary General Mirza Fakhrul Islam Alamgir made the comment over recent statements made by Awami League senior leaders, including Prime Minister Sheikh Hasina, during a press meet on Monday.
"The government has appointed Abdul Kahar Akondo, who also happens to be their party leader, as the investigation officer. He made the chief suspect in the case Mufti Hannan to make a confessional statement only because they want to use the issue to dominate and weaken their main opposition party. But Hannan has withdrawn his statement and brought the conspiracy of the government into the light," he said.
"Now the government is using the judiciary to carry out their political will. We strongly condemn it and urge the government to ponder the toxic situation it will bring into the national politics."
The grenade attack on Aug 21, 2004 at an Awami League rally on Bangabandhu Avenue in Dhaka left 24 people dead including, central leader Ivy Rahman. Awami League President Sheikh Hasina survived the attack but suffered a hearing impairment.
At the time BNP Chairperson Khaleda Zia was the prime minister, while Sheikh Hasina was the leader of the opposition.
"There is no doubt that Khaleda and her sons were actively involved in the attack," Prime Minister Sheikh Hasina said at a party event marking the anniversary of the grenade attack.
The case filed over the incident accuses Tarique Rahman, former deputy minister Abdus Salam Pintu, and former MP Kazi Shah Mofazzal Hossain Kaikobad.
The state counsels have said the date of verdict will be determined by September once the testimony of suspect former state minister for home affairs Lutfozzaman Babar is completed
The BNP has said that recent comments by the prime minister regarding the involvement of the BNP chairperson and her family are attempts to influence the verdict.