It is not established that either of them stepped in blood.
It is not even established that the footprints were even blood, let alone blood from MK.
You keep on repeating this as though it is fact when it is speculation. It is NOT supported by any evidence at all.
For all you know, these "footprints" could have been made a hundred years ago.
The main problem is that you have a fundamentally flawed idea about what luminol reveals. The flouresence can be made by many other substances, blood is not the only one, and most of those "false positive" substances are common in residential areas. The way it works is that luminol shows were blood *MIGHT* be. To show if it actually IS blood, you have to do confirmatory tests. In this case the confirmatory tests were negative. If the confirmatory tests had come up positive, the next thing that would be necessary is to show that the blood came from MK. That should be simple to do, because, if they claim to have identified AK DNA in these "prints", then MK DNA should have been there in abundance. Further to that, you have to establish WHEN these prints were made, since they were only collected considerable after the crime when large numbers of people had been tramping around the scene. None of these things were done or yielded positive results, and the obvious conclusion was that these "prints" were neither blood nor did they came from MK. If the prosecution wants to make the case that it was blood, and that it came from MK, they have to provide EVIDENCE for that fact, and they have failed to do any of that. The can't just make the claim it was without showing that it actually was so.
The way science works generally is that people come up with a hypothesis and gather data to support that. Very often you will get such data, but for those results to be valid you have to perform something called controls. Basically these are test experiments where you systematically use known samples to eliminate all other possible explanations for the data you have observed. This is often not done properly in scientific studies, which is why there are many junk studies in the literature. People get tunnel vision and don't ask the questions to consider possible explanations outside of their theory. They lack critical thinking. That is exactly what has happened and is happening in this case. This kind of "non scientific" thinking is very prevalent among CSI personnel (who generally don't have much a solid scientific method training to begin with), and it gets even worse when their results get into the hands of LE or prosecutors who are even more poorly trained in interpreting the data. This is why we get so many false convictions.
