Pakistani intelligence groups were involved in the attack that meant to take out then the opposition chief Sheikh Hasina, said Chief Prosecutor Syed Rezaur Rahman during the second day of argument at a Speedy Trial Tribunal in Dhaka on Tuesday.
The conspirators that included "communal and likeminded political parties especially the Four-Party coalition headed by the BNP and Jamaat-e-Islami" were angry with the Awami League for pursuing secular politics, he said.
"Local and international militant groups especially the Lashkar-e-Taiba, Tehreek-e-Jehad-e-Islami and Hizbul Mujahideen and Pakistani intelligence ISI (Inter-Services Intelligence) together planned the attack on Aug 21."
The case filed 13 years ago passed many barriers to reach its final stages. Arguments began on Monday at the end of which the verdict will be scheduled for delivery.
Twenty-four people died and several more were injured after grenades were hurled on an Awami League rally in front of the now ruling party's offices in Gulistan's Bangabandhu Avenue.
Central leader Ivy Rahman was killed. Party President Sheikh Hasina, now prime minister, narrowly survived but suffered hearing loss from the blast sound.
The BNP-Jamaat government that was in power during the attack had interfered in the attack's investigation.
The case's chargesheet was filed during the regime of the army-backed caretaker government. It accused 22 individuals including Harkat-ul-Jihad leader Mufti Hannan, militant leader Md Tajuddin and his brother Abdus Salam Pintu, the former BNP deputy minister.
Jamaat leader and former social welfare minister Ali Ahsan Muhammad Mujahid, former state minister for home Lutfozzaman Babar and former BNP MP Kazi Shah Mofazzal Hossain Kaikobad were also accused.
"Then deputy minister Abdus Salam Pintu and state minister Lutfuzzaman Babar had enjoyed good relations with Tajuddin who studied in a Pakistani madrasa. They planned the attack together," said prosecutor Rezaur.