First of all ‘News’ is not objective and impartial, it is a socially manufactured product because it is the result of a selective process ( McQuail- 1992)
Editors, journalists, and sometimes owners (gatekeepers) make choices and judgements about what events are important enough to cover and how to cover them.
News selection is bias because it depends on the following- Routines : Newspapers and TV coverage is shaped by the routines and organisation of the companies themselves. The collection of news itself as well as its presentation might then be bias before it is even reported. Finally the story must be percieved as newsworthy.