No.
What does that question have to do with hard Mars aspects and serial killers?
Charles Manson has a Mars-Neptune conjunction. I consider that to be a hard aspect. Bill
Clinton has one too.
It is interesting that such a large percentage of serial killers have a hard Mars aspect.
But frankly, I think you are making Much Ado About Nothing, stirring up a hurricane in a teaspoon.
Mars has been associated with war, violence, force, compulsion, killing, blood, piercing instruments, high passions, brigands.......ever since the Beginning of Time.
I have a very strongly afficted Mars. He is at the focus of a massive T-square, squaring Sun and Pluto. He is conjunct Saturn. He is in his detriment. I step over ants and beetles in my path, not wanting to harm an innocent creature. Can I be cold, cruel, deadly? Sure, the potential is there. After all, I belong to the most violent, bloodthirsty, savage species to have ever walked the face of the Earth.
Some hard aspects to Mars produce excellent blacksmiths...or engineers, butchers, surgeons.... These people need the "force, violence, cutting nature" of Mars to perform their functions in life.
The same aspect present in a matrix (chart) inclined toward murder and mayhem may act that way. But only -- ONLY -- if that chart -- AS A WHOLE -- points in that direction. The hard Mars aspects you see in a high percentage of charts belonging to serial killers is only one factor that must be present to produce such a monster. It is only one of a combination of factors that must be present.
I saw in one of the replies in this thread that "Mercury will control Mars by thought...." But what if Mercury is distressed, distorted, etc.? This is the same kind of simplistic thinking as assigning serial killers to hard Mars aspects...
If we are to become competent astrologers, we must learn to read the chart as a whole.