Speaking from experience...
... there's not another film about a murder that hits as close to home as this one for me. When I was in my early 20's, I got myself mixed up with the wrong guys. One of those guys is now in prison for murder, and I was very, very nearly his first victim. The horror of that memory is real to this day, decades later. This guy stole 800 dollars from me, and was very worried that I knew he did it. I pretended I had no idea he did it, because the idea of what he was capable of was very clear to me. He took me out for a drive -- a drive I was terrified to refuse -- and led me out to an old cemetery, and asked me to lay down and look at the moon so he could tell me a story. I remained as calm as I could, made jokes, and kept the conversation as light as a could. Finally he asked me if I thought he was the one who stole my money (which I knew then, and later confirmed, he did). I put on the most surprised look I could and said it was ridiculous to think that, since he was my best friend, and I know he'd never do anything like that. The whole time we were laying there talking, he had his hand inside his jacket, and I knew he kept a big hunting knife in there.
A week later his slimy friend told me that our mutual "friend" did in fact steal the money and that I was lucky to be alive, and that he almost killed me that night. I left the state the next day.
That night in that cemetery -- although no one actually ended up dead -- echoes for me very hard when I watch The Onion Field. I'm still haunted by emotions when I remember that night. It's a horrible, horrible feeling.
No other movie brings those feelings back home for me like this one does.