That's terrible, but don't blame yourself for not noticing. Especially if its something you don't expect like someone dying that young.
It's not like many of us know what the stench of a dead body smells like.
In my case someone was murdered by her ex next door and I didn't hear a peep (including the police and ambulances with sirens wailing) because I went to bed early that night.
I found out a day later when a co-worker texted a picture of my front door he had seen in the news. Another neighbour gave me the details about the terrible screams and everything.
What's even more dark is that she suspected it, so she recorded her own murder as evidence with her phone.
The police had already arrested her ex at the scene but they were sort of curious about my alibi that I had slept through everything on a saturday at ~11 PM - 1 AM when I was first asked.
Until they tried to wake me for some follow up questions at 8AM for 3 days and eventually gave up and decided to try on Sunday at 5PM when I left to visit my parents like I usually do.
"We knocked really loud on 3 different mornings, your car was there but you weren't home? Are you working night shifts?"
"I'm sorry officer lady I literally sleep through fire alarms going of in my bedroom and apparently murders too"
On day 3 they send 2 guys with 'loud voices' to see if that would work.
I felt bad about not hearing anything because they were trying to get this guy on a pattern of abusive behaviour.
They needed to back up a few claims by another witness who talked about slamming doors and the screams and whatnot before the event but he had some psychological issues himself.
Because it was an early Saturday night most people weren't home. Fortunately his testimony held up in court and they found the recording on her phone.
