Lots of religions and/or families don't especially take kind to autopsies. And at the time, Charles's kids and perhaps most of Lori's relations had little to no reason to suspect murder. It's not unheard of for people of her age to suddenly experience a lethal event from a stroke or brain aneurysm.
I have known four people who did just that. A family friend best known through my uncle died instantly of a brain aneurysm while he was on a family outing; he was very athletic and a great dad with a great job, he literally just fell over dead in front of everyone, at only 46. Second one was my grandma on my father's side, she was cleaning her bathroom at 53 and just all of a sudden got the worst headache of her life and called an ambulance. She lived but was never the same. The third time a professor I very much like died at 38 from a sudden, massive blood clot rupturing while doing his morning jogging. And the fourth time was an old friend of my grandmother on my mother's side, she turned her head while parking her car and died after a few hours from cracking her neck while looking behind herself, causing some sort of blood clot to dislodge and move onto her brain.
Point is, death is something you can experience at any age, but the older you get, it does seem that it's more frequent and random sometimes...