You could flash freeze people. The problem with any freezing is that when the water inside cells freezes, it becomes ice. Ice crystals are pointy and ice takes up more space than water, so the ice can rupture cells.
To stop the ice from killing the person's cells, you can flash freeze them. Flash freezing makes smaller ice crystals than normal freezing, decreasing the number of cells that rupture. However, ice is still less dense than water and therefore takes up more space in the cell, meaning the cell might still burst. To stop the cell from bursting, you can dry out the cells (warning: do not use on live humans). This is not an option unless you want human apricots. Instead, you can attempt to equalize the pressure on both sides of the cell membrane.
If you immerse a human in a tub of water and flash freeze them, (hopefully) when the water in and out of the cell will try to expand and find that they can't because the pressure of the expanding water on both sides is equal.
To do this, the water surrounding the cells and the water inside needs to freeze at the same time. If one freezes before the other, the ice will rip the cell apart. To get any pressure, the tub must be fully enclosed and built with something strong enough to resist the pressure of the expanding ice. If the tub is not enclosed the ice in the tub will have room to expand and will not push against the water inside the cells. If both of these conditions are met you will have a frozen human. It shouldn't matter what unfreezes first, because then the volume of the water/ice will decrease. If you perform the procedure wrong, the cells will rupture and it is best to keep the person frozen if that happens so you do not have any legal issues until you have called up your lawyers and prepared your defense.
To quickly melt the ice, you can expose the person to a vacuum, which will make the ice around them sublimate almost instantly and probably kill the person but do what you wish.