Simplify the following text for a Grade 9 native English-speaking person.
Original: Founding father of Bangladesh , Sheikh Mujibur Rahman was assassinated in 1975 by pro-pakistani army group and thus enabled army chief Major general Ziaur Rahman ( a former BAKSAL member of Sheikh Mujibur Rahman `` Book Source : Tinti sena Obhuthan by Colonel Hamid '' ) to seize power .
Simplified: However Sheikh Mujibur Rahman was assassinated in 1975 and army chief Ziaur Rahman seized power .