I saw a pic of it on the Hitler Channel the other night and there is no way it went through two chests, a forearm, (hitting a bone) and a thigh and came out intact.
The tissue attached to the flap is undoubtedly brain tissue that fell off and was hosed out later. The rear of the limo and a motorcycle patrolman were covered with blood and brain/skull fragments. It cannot be totally explained by the speed of the motorcade.
I know enough about ballistics to state that solids penetrate and hollow points explode. I'm not a pathologist but I've spent 10,000 hours in trauma situations, including battlefield conditions.
I am not a pathologist but I ran a gun shop for a number of years. Guns are just sophisticated rock throwers.
In actual fact, hollow points don't necessarily "explode" they merely increase their cross sectional density on striking and penetrating the target by expanding larger than the original bore diameter. This has several effects:
First the bullet becomes larger and a larger hole can do more damage.
Second, the projectile will slow down faster because more target material is impacted so more of the momentum of the projectile will be transferred to more material.
Third, the projectile will have less of a tendency to penetrate and pass through the intended target to hit unintended innocents standing behind the target. A bullet that passes through the target is inefficient because it still has unexpended energy that was not been applied to the intended target.
Hollow points are designed to increase "stopping power" or, alternately, to transfer more of the energy contained in the moving bullet as momentum to the intended target.
If you want explosive effects, an interesting explosive effect can be created by putting Fulminate of Mercury in the hollow of the bullet...
Frangible bullets are designed to break apart and do as much damage as possible. They are designed more to kill than to "stop."
Solid bullets are designed to wound a target. Killing is an undesirable side effect. A wounded soldier removes THREE enemies (one injured, two to carry him) from the battle.