A good concept to focus on. There's a psychological edge driving this narrative and gives it an intriguing dimension. Who killed who, indeed? Is the victim or murderer speaking?

A few phrasing issues:

'my arms hand by my sides' - I'm not sure what this means?

'scarlet thoughts' - a bit literal for someone referring to a mental state

'some seeming to change each time that I look' - I think 'appearing' might be a better substitute for 'seeming'