Of all the causes of deaths, violent deaths probably account for 2 -3%. Intentional homicides globally account for less than 1% of all deaths, though in some countries it can be as high as 10%.
Some murderers kill more than one person. Say 2 of every 10 murderers kills two (10 murderers = 12 murders). That gives us 410,000 fresh murderers every year. Let us further suppose that murderers are 10 times more likely to be murdered than the general population. Even if we take the worst country homicide rate of 50/100,000 and assume that murderers are killed at the rate of 500/100,000, this only rids us of 2,050 murderers annually. The clearance rate of recorded homicides globally is probably less than 50%. However, clearance rates don’t affect the number of murderers in our midst. Execution rates are so low as to not be significant in reducing the growing population of the world’s murderers.
The incontrovertible reality is that we add over 1,000 murderers to the population every day.
Estimating how many murderers are around is more uncertain, but the arithmetic says it should currently be around 25 million (35 / 100,000 of population). To put that in perspective, any cricket match with 30,000 spectators would include 10 murderers in the crowd.