dead and buried within 10 years
If we're talking about a longer period of time, such us 10 years, and a bigger city like Lodz, with many ambulances, you could quite easely calculate
how many people were murdered by these two ambulances using simple statistics.All you need to know is how many ambulances there were in the city of Lodz within these 10 years, how many patients were transported during that time, how many of them had died during the transport. That would give you your average death rate in a Lodz ambulance. If there is a difference between that number and the number of deaths in our "suspect" ambulance, we can calculate the standard deviation, which is a square root of variance, or basically probability that this one ambulance's death rate is higher then average.
For example, you could say that an average death rate for a Lodz ambulance is, let's say, 8%, and the death rate of our "suspect" ambulance is (just an example!) 24% with a standard deviation of +-2.6%. Then you could say, that the chance of the "suspect" ambulance having so much higher death rate simple by "bad luck", not a homicide is 1 in 160, or 0.6%. That gives you the chances that a homicide had occurred is 99.4% and you have your number of murders +-2.6%.