Omitting facts that are utterly irrelevant is not lying by omission. The media doesn't report what he ate for breakfast or which brand of clothing he buys either.

People's religion and political views aren't generally considered relevant to a homicide unless there's an indication they had something to do with the motive, at which point they get reported. Otherwise, the media sticks to basic biographical details like occupation and family status.

Otherwise, the media gets accused of sensationalizing things, implying someone's religion is relevant to stir up controversy, etc.

If it turns out this was either a hate crime or a politically-motivated crime, do you really think the media will suppress that? Spoiler: they don't.

Lying by omission has a specific requirement that the liar knows something relevant and chooses not to disclose it. That’s quite different than refraining from speculation about the killer’s motive.