The storming of the parliament was in response to the actions of police and élite forces who allegedly beat up protesters who were marching on the Prime Minister's house asking for his resignation. Several protesters were injured in the earlier march.
Although some activists have been holding protests since March this is the first violence since last December when elite forces also are charged with beating up protesters. The prime minister as well as many MP's have been accused of corruption.
Attempts to have corruption investigated and stopped have been thwarted. The premier Sabah has been a constant target of criticism. The foreign minister resigned a month ago. He had been involved in a plot to put money into foreign accounts. Sabah is an important member of the royal family and many believed he was also involved in the plot. For more see this article.