Has L Ever Seen A Shinigami Before In His Youth?

 **Before I start this,yes I am very well aware that in the anime,L is shocked to know the Shinigami exist and he has seen Rem for the first time later on. But keep in mind that a theory is a theory and not an official source of information. Everything said in the theory is through my own perspective.**

Have you ever feel strange that L somehow knows what a Shinigami is? Even before meeting Rem,he thinks they are real. Upon hearing that word,he seemed freaked out over the fact they do exist. But what if he freaked out because he was right to begin with? Did he ever experience something in his youth that involved a Shinigami? That's what I am looking through in the theory.

The Shinigami may have been in the Human World before

Yes,i'm ignoring the fact that Ryuk was the first Shinigami to come to the Human World prior to the series. But what if Ryuk was'nt the first Shinigami to do so? Maybe a Shinigami went to the Human World a long time ago for possibly better view the human life. The Shinigami may have been seen by a certain little human,L. He approaches the little human without any conscience. Of course,like any kid would react,L is very curious of this mysterious being. As the Shinigami begins to give a Death Note to L,the police force arrives at the scene and shoot at the Shinigami,causing him to flee. Years later,L somehow remember this very day. He wanted to prove that they are indeed real,but no one ever believed in his story,claiming he made this up.

Beyond Birthday and the secret behind his eyes

In a previous theory,I suggested that Beyond Birthday may have been L's twin brother. Since Beyond Birthday has been confirmed to be born with Shinigami eyes,L may have probably knew about this. But so does Mello,but why? L must have told him about it. Is there a reason why L is destined to solve the Lost Angeles BB Murder Case? Yes,it could have been a reason. L is known to be a very smart detective. Researches may have helped him at the time. He probably searched up information about the Shinigami and the eyes. Maybe what he has found further confirmed his thoughts about Beyond Birthday.

The surveillance cameras

If you recall in the series,L has set up 64 cameras into the Yagami's house in hope of catching Kira. What if he did catch something on camera that seemed suspicious to him? Is it possible he may have seen Ryuk to begin with without telling anyone? It could be. L has a thing for not telling anyone about certain information he knows,and it makes sense. Maybe the presence of the apple floating in the air and disappearing gave him a hint on noticing Ryuk. 

Light talks to himself or not?

Think about it. L notices Light possibly talks to himself some time to time. But what if L finds it suspicious he do so? Surely he don't think it's normal. He knows Light is talking to someone,even if he don't see it. He knows something is up. 

Catching Rem

After touching the Death Note and finally sees Rem,L could'nt believe his eyes. Yes,the Shinigami are real and he was right. He meets up with Rem so she could tell him how the Death Note works. What he doesn't know,is that someone is willing to kill him.. Or does he? After Watari's death,L was willing to try and capture Rem. Why does he thinks of capturing her after the death of Watari? Because he knows Rem is responsible of killing him. He knows she used the Death Note. He wanted to capture Rem so she would'nt kill anyone else. This is why he told everyone to look for her as soon as they can. However,it was too late. Rem kills L before he could capture her.