It seems I screwed up and killed the guard that you're suppose to report to. I was wondering, is this a crucial quest? I've already beaten Skyrim before and have done this quest but I just can't remember if it was actually vital to the campaign of the game or obtaining any important items? Anyone remember? Thanks.

Only two things buying the house in Windhelm and the necromancers amulet. I can't think of anything else.

well i think you need it to buy the house... if you are on pc use console press the guard and "resurrect" on him if you are on PS3/Xbox360 do load or continue to play like this and do the Civil War Quest i think you can buy the House that way too. The only problem i see it is maybe not solving the murder. Or you can follow the blood to Hjerim, ask the woman there or ask the steward if he needs help, thats all i can remember.

Can you try to reload a previous save?

Thanks Areial and DarkDragonsElf. I guess I'll just wait it out and see what happens but at least it's not TOO major. I can live without a home in Windhelm. ShadowTitan17 I do have all my saves since the first quest but it happened so long ago it's not even worth it. Thanks for the info everyone!