Police have confirmed they have released the truck driver from custody and is still assisting police.
His 22 year old passenger remains in custody this morning over other matters.
The driver of a truck that caused yesterday's fatal collision in Pimpinio remains in police custody.
The 36 year old man from Murray Bridge in South Australia was driving the B-double truck along the Western Highway when its trailers dislodged around 2am yesterday, which then collided with the Ballarat-bound Firefly bus, killing the bus driver.
Police say the truck driver along with his 22 year old female passenger are assisting police with their enquiries.
The Western Highway between Horsham and Dimboola has since re-opened this morning after police wrapped up their investigation at the scene.
Image via Channel Nine.