Is it a crime to not report a suspected crime?

Few nights ago, my neighbor was killed by her husband. We live in a building, they were doors next to mine. That night I heard them arguing a little more harshly then usual (they were often arguing) and I didn't call the cops. It was late and was sleeping but I did hear them. At one point I heard a loud bang like someone hit something, but I thought it was just a smack on the table (you know like out of rage or something). I was just pissed that I couldn't sleep, and I did think about knocking on their doors to tone it down, but in the end I decided to ignore it. It stopped eventually and I fell asleep (or maybe I was just too tired and sleep got me sooner).
Then police knocked on my door in the morning wanting to question me because there was murder. Apparently the husband hit his wife and as she fell she hit her head and died. He confessed. They asked me if I heard something and I told them all I said here. But I feel so guilty now. If I called the police sooner this wouldn't happen. Like, I knew they were at it roughly and I just ignored it. To be honest I don't even know if police would came just because of noise, they usually reject those calls even you didn't give the warning to the neighbors first. Also part of me was kind of scared of knocking on their door because they were in the heat of the moment and maybe I would also get hurt. I thought it wasn't THAT BAD to call other neighbors, I mean there are families with big guys around, I thought maybe they would interfere eventually if they heard them too. But apparently no one heard anything.
I feel so bad I can't stop thinking about it. I freaking saw the husband almost every day in the hallway, he did seem off a bit but nothing too alarming in my opinion. I think about what if it was me? If someone beat the shit out of me and my neighbors ignored it? I believe I did a crime.
Is it a crime to not report a suspected crime?
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