What caused rumors that Taizu had been assassinated?

Rumors that the Taizu emperor was assassinated stem from the suspicious circumstances surrounding his death and the subsequent succession of his younger brother, Taizong.1

When Taizu died in 976, the throne passed to his brother, Taizong, rather than to Taizu’s own son. This departure from the expected line of succession led to speculation that Taizong had seized the throne against Taizu's wishes. These suspicions were further fueled by the behavior of Taizong after he became emperor; he treated his younger brother and his nephew with such cruelty that both were driven to commit suicide, casting doubt on his character and the legitimacy of his rise to power.1