A Hard Day

Ko Geon Soo, a corrupt detective whose mother recently died, drives away in the middle of the funeral, having been informed that his squad is being investigated by internal affairs for bribery. He crashes into a homeless man who wanders onto the road, killing him. Fearing manslaughter charges, as he is intoxicated, Ko declines to call the police and hides the body from a passing patrol car. With the body in his trunk, he returns to the funeral and manages to seal the body into his mother's coffin while escaping detection. But someone has been watching all along, and Geon Soo gets a mysterious call from a person claiming that he was the sole witness to the crime, who now begins to threaten him.
(Source: Wikipedia)