I see what you mean now about the difference - having both the murderer and the murdered within one's family.
I suppose if one believes the media are driven by genuine sensitivity for the feelings of people they write about, then it's possible to believe they chose the terms they used because surviving family members experienced something which made the case more worthy of the description "family tragedy" than in other cases. I don't happen to believe the media are driven by sensitivity or care for the feelings of anyone unless doing so will increase their revenues.
When a person does something horrible - a serious assault, a sexual assault on a child, killing someone, an act of terrorism, yes it is natural that the family and friends of the person will struggle to come to terms with what happened. They, too, may find it hard to square up their experience of their loved-one as gentle, sensitive or other positive qualities with the terrible act they committed.
But, in my experience, we don't see the press reporting accounts from families of all perpetrators in the same way. Particularly where the press have chosen to demonise the perpetrator, they frequently will vilify the family as well, at least indirectly. Often they will dig in to the person's history to find "reasons" for why they became evil, often centred on what they report as family "dysfunction." Remember some of the descriptions of the families of the two boys who killed James Bulger?
Basically, if they've decided a person is a "baddie," they'll scratch and scrape for evidence, rumours, statements from "friends," etc., whatever they can find to support their assertion.
However, if they have decided a person isn't really a "baddie," they'll similarly scratch and scrape for anything they can report that can counterbalance the horror of the crime they committed.
The media just aren't that keen for fathers, especially those who don't "fit" the template for "villian" (e.g. immigrant, substance misuser, long-term unemployed, criminal record, etc.) to be lumped into the "baddie" group, particularly the papers that witter on about upholding family values and traditions, etc.