It is imposable(unless it hits your eye, but you would have to be looking straight up) for a bullet to kill someone in true free fall. If it is fired with any angle then it can kill on the way down. But true free fall, by a bullet fired straight up in the air will not kill someone on the ground. The terminal velocity of a bullet will not kill you.
Sorry, that is incorrect. It most certainly could kill a person, coming straight down, depending on a variety of different factors:
Did the bullet turn around due to wind or bullet contruction such that the nose rather than the base is heading down first on the way down? If nose first, then what is the BC of the bullet? BC applies in cutting the wind straight down too. The higher the BC, the higher the terminal velocity from gravity. Also, the higher the BC and the highly-correlated SD, the higher it's penetration ability through the skull, so again, depends on whether the bullet turns around, and to what extent it turns around, and the BC. Also, if it does NOT turn around, then what's the BC of the bullet's BASE (which at that point becomes its nose)? Is it a boattail bullet, which will then have a higher BC than a flatbase?
Next, what's the weight of the bullet? The heavier the bullet, the deadlier, due to sheer momentum, which can translate into more penetration and crushing of skull bone. Further, regardless of whether it penetrates, the sheer weight concussing the skull can cause brain trauma or death, due to the massive jolt, if the bullet is big enough. Is it a 700 gr 12 ga slug? 750 gr .50 bmg? Going terminal vel? Are you kidding - death would be more likely than not.
Next, what's the bone density and resiliency of the person in question? Is it a baby getting hit in the soft spot? Is it a young person with flexible bones but not very thick and hard bones (skull)? Is it an elderly person with osteoporosis?
Next, is there any downward wind shear force aiding the bullet's velocity with a "tailwind"? Wind goes in all directions, not just left and right on a 2-dimensional scale. Many factors come into play, and I assure you that a bullet in the brain can be deadly, and there is a high probability that a given bullet will penetrate a skull.
Lookit, there is no magical sharp distiction between a bullet shot directly up at 90 degrees with a plum, versus a bullet shot at 89.999995 or 90.000005 - that's got nothing to do with it. Any bullet in the *general* range of 80 to 100 degrees, give or take, as far as the horizontal vector goes, is going to have a VERY minimal amount of a horizontal energy/momentum, from that particular vector - the damage comes from the bullet more or less stopping at its apex, turning around and coming down at its terminal velocity (if it has enough time to reach terminal, which most any bullet would). There is no magic distinction on either side of 90 degrees. At SOME point along the scale, the horizontal vector is low enough that momentum/energy is carried horizontally, at least until that point near the very end of the trajectory, where the parabolic curve is such that the drop rate is much higher than horizontal momentum, due to energy bleed from air resistance.