It was a haunting melody, full of rises and falls. John had never heard it before, and assumed that Sherlock was composing it himself, and that it was following the twists and turns of his thoughts.

John stayed silent, letting his own thoughts drift, when Sherlock's voice broke him out of his reverie.

'Do you remember that liquid that was on the floor of the janitor's closet? I had it tested at the lab. Turns out it was the bleach from the bottle. Just as I thought.' There was a pause as the music reached a crescendo, which seemed to be applauding Sherlock's progress in the case.

'Lestrade thinks that the bleach was deliberately poured over the dead body by the murderer in order to remove any DNA or fingerprints he had accidently left on the body. It seems logical, don't you think?' replied John once the music had settled again.

'If Lestrade is right, how can you explain why the floor was still wet when we arrived? We know that Anderson didn't do it, because his fingerprints aren't on the bottle. It's certainly doesn't take 5 hours for bleach to dry.'

John was silent. He had nothing to counter Sherlock's point with. He decided to just let the bleach problem figure itself out and let Sherlock continue bouncing ideas off him.

'What is easier to understand, is that paper you found. Turns out you probably found the second most important paper there was. It's the fourth page of Martin's notes on that wife/husband murder case. Turns out, it's not so straightforward as everyone believes.'

'Well, that explains why Rob Martin was at work last night.'

'Indeed it does. The paper outlines that there were unexplained blood splatters on the wall. They weren't from the wife or the husband. That much is commonly known. What isn't known is that Martin had discovered whose blood splatters they were. He says on the paper that it changes the whole case. The husband is innocent.'

'And the real murderer?'

'That is unfortunately on the next page. As I say, you found the second most important one.'

'So you think that you have found a possible motive? Martin was killed because…'

'He found something that should have remained hidden. He was silenced in the most permanent and effective way.' Sherlock had interrupted John, but he didn't mind. Sherlock was the smart one that had figured it all out, and deserved all the credit he could get. Even if it was only from John.

'There's something else too. That red pen I found, Martin was using it when he died. He must have been editing his report and was going to hand it in, when morning came. There are red scribbles all over that report. Including a big 'WHY?' in the corner. He obviously had potential, this Rob Martin. It's a shame he died really.'

'So you think the red pen might be able to lead you to the murderer?'

'Hopefully. That's where I'm off to now. I need to analyse it at the morgue. There's no need for you to come. Make yourself a cup of tea or something pleasant.' The music abruptly stopped, and Sherlock grabbed his coat and scarf before leaving the cosy apartment and calling a taxi. John sighed. He would have liked to listen to more of that violin. At least Sherlock was right about one thing. A cup of tea was exactly what he needed.