In the video, Aug 21 grenade attack suspect Mufti Hannan is heard saying that the BNP chief was involved in the attack to eliminate his mother, Prime Minister Sheikh Hasina.
He posted the video of the statement around 9pm on Friday, the 11th anniversary of the attack on an Awami League rally at Bangabandhu Avenue that left 24 killed.
Joy wrote in the status: "August has become a very dark month for us, especially my family.”
His grandfather Bangabandhu Sheikh Mujibur Rahman was assassinated on Aug 15, 1975 with most of his family members.
"On this day in 2004 my mother was almost killed in a massive grenade attack. 23 members of our party, including Mrs. Ivy Rahman, wife of our former President Zillur Rahman, were killed and over 400 injured.
“This was the 19th assassination attempt on my mother," he wrote.
He also alleged that that Khaleda's son and Senior Vice-Chairman of BNP Tarique Rahman was involved in planning the attack,.
In a programme to mark the carnage earlier on Friday, Hasina alleged that Khaleda and Tarique both were involved in the deadly attack on the Awami League rally.