Break ties for first place by who killed first

At the moment, when two people are tied for a place on the leaderboard, the order they receive their spot is seemingly random.

For example, I kill the infected and I’m currently ranking first. If someone else kills the infected and they have the same kills and deaths as me, they can still end up in first place.

I think that this issue should be solved by having the most recent kill timestamped to make the one who got to that spot on the leaderboard first maintain it.