I have to say that I'm utterly perplexed by the notion of a .22 LR somehow doing more damage, in general, because of its relatively high probability of ricocheting off bone in comparison to larger calibers. A bullet only has so much momentum and will only penetrate a certain maximum distance through flesh whether it is deflected or not, and one would think that deflections would rob some of its momentum, thereby reducing penetration overall. Whether it penetrates in a straight line or a zigzagging path, the real harm it does depends on what happens to get hit. Also, while a tumbling .22 LR bullet will cause more damage to the depth at which it penetrates, that depth will necessarily be reduced because it will lose momentum more quickly. This is all based on physics--there is no magical way for the .22 LR to do more damage than its limited energy will allow. All you can do with bullets in general, aside from aiming them accurately, is make sure that their energy is used optimally rather than wasted, hence the development of hollow-point bullets in calibers that would otherwise likely overpenetrate and thereby waste much of their wounding potential. The .22 LR is not such a caliber against human-sized targets, and while it's lethal, it's neither inherently more lethal than larger calibers, nor will it liquify one's insides by bouncing around 20 times and penetrating several meters of flesh in the process, please.
In the specific case of shooting a .22 LR bullet into somebody's head, whereupon it will, according to some, bounce around several times and thereby scramble the person's brain more than a larger-caliber bullet would, I can't say that I know all the facts but I'm skeptical because I know of a number of cases where people survived penetrating head shots from .22 LR handguns, at least for a few hours or days. There was a guy who shot himself in the head in my neighbor's front yard a number of years back, being so distraught (more like in a murderous rage) at getting dumped by my neighbor's daughter, while I watched discreetly from my front door, ready to call the police (had I known that he was armed, I would have called already, but his gun was in his car). He died two days later in the hospital, if I remember correctly. I'm not exactly sure what damage was done, but there was definitely no exploding exit wound with buckets of blood and bone fragments spraying all over my lawn. With no hearing protection and from fairly close proximity the shot sounded like a small firecracker. Now imagine somebody's head getting hit with a .40 or .45 with the muzzle pressed against it--all that energy released into the relatively inelastic tissues of the brain, and probably expelling some nice chunks of it out the other side, too. Are people still convinced that .22 LR is the most lethal caliber for head shots? As others have said, its main advantage--especially for assassins--is that it is relatively quiet, and with the latest technology can be suppressed to near silence.