The son of a former Bangladesh prime minister went on trial in absentia on Wednesday over charges he was involved in a 2004 attack that killed at least 20 people and injured the current prime minister.

Tareque Rahman, 46, the influential eldest son of Khaleda Zia, refused a court summons to return to Bangladesh from his home in London to attend the trial in Dhaka.

Rahman is accused of criminal conspiracy in a plot to kill his mother’s rival, Sheikh Hasina, and her party officials, state prosecutors said, adding that judges had adjourned the case until April 9.

Hasina was addressing a rally in Dhaka on August 21, 2004, when several grenades exploded, leaving at least 20 Awami League officials and supporters dead.

Hasina, then leader of the opposition, survived the attack but was severely injured in one ear. She returned to power in the 2008 elections.

Rahman is alleged to have hosted meetings planning the assassination attempt. His lawyers say the case is politically motivated.

The families of Hasina and Zia have competed for power for decades in Bangladesh, with street clashes often erupting between their rival political parties.