Erzhan Utembaev, the former head of the Senate administration, reiterated that he was not fully conscious when he wrote President Nursultan Narzarbaev a letter in which he confessed to commissioning the murder.
The case is being held behind closed doors in Taldy-Qorgan, some 250 kilometers north of Almaty,
Sarsenbaev, his bodyguard, and his driver were found dead on February 13 in the Almaty region.
In addition to Utembaev, nine former security officers are being tried for their alleged involvement in the triple murder.
Opposition leaders in Kazakhstan believe more senior officials are behind the killings.