I had a dream a couple of nights ago where I killed a stranger, does this signify anything?

Dreams do not mean anything psychologically. The leading hypothesis amongst psychologists to explain dreams these days is called the 'activation-synthesis hypothesis,' and the basic idea is that the lower, simpler parts of your nervous system fire random impulses into your higher thought areas, and a dream is that area's method of making sense of those impulses by constructing a narrative around them. It's entirely random, nothing you see has any real significance, and it's not worth worrying about.