they dont have a history of mental health problems.
If they had, you'd be more aware of the fact that it's not uncommon for people with mental illness to avoid contact, not answer phone calls, not answer the door (if you can get there in person).
From the article he sounds really quite unwell. He may well have been hard to get hold of, hard to make sense of, not particularly trusting, not able negotiate the benefits system, not wanted to try to tap family for money if they were not well off, or were frightening to him. And so on and so forth.
People with mental illness can be incredibly vulnerable and simultaneously incredibly hard work for those attempting to engage with them.