I'm having difficulty in understanding exactly what happened. It's aresult of journalists writing about construction, so I'm going to go at this in two ways. I know some Canadian Safety workers read this so if and when you get better details, please add them or contact me and I'll post what you get.
The common claim between articles is that the form slipped out of the rigging. Guys love to rig using "basket" rigging practices. It's quick and easy and you look like you are fast. While chokes take longer, weaken the rigging capacities, and it annoys people to do it, I prefer this method of rigging. Basket rigging allows the load the freedom to fall out of the rigging. If you are hoisting outside of a building from the ground to the top of a 20 story and don't have a lot of real estate to work with, if you hang up on anything with a basket the load can be ripped out. If you have a choke in place the load has a much better chance ot remaining locked in.
If you use a choke the center of gravity is not as critical a componenet because the rigging is less likely to run. They mention winds here as having come up. If you get into winds with an uneven load in a basket and it starts to spin, the load running becomes much more likely. Proper planning for the job will allow you to get rigging with sufficient capacity to allow chokes on any load.
The other potential cause here would be a lifting eye or rigging failure. Beyond consistently checking and inspecting your rigging, I don't have much to add here without specific information.
I don't think that this comment will apply here, but since we are talking about concrete panels... They are often stuck to the deck or wall. on modern cranes operators should get used to what a piece weights because he's going to hoist it over and over. You should not be freeing the load with the crane. The carpenters, or whomever, should be sure that the load is loose by the operator having the approximate weight then the load should be Burke barred or levered to assure that it isn't stuck or break it loose. The load should also be lifted slowly until you are certain no nails or tie wire is still attached and not about to hang up.
A man is dead, and we are likely able to improve as a result of it. We owe it to his memory to find out what it is that we need to do better to prevent the next death.