Do SSD's present a forensic challenge

Forensics investigators and hard drives have developed something of a mutual understanding over the past couple of decades. That is, if we connect them to a write blocker, they’ll tell us everything they know and there is zero chance of them changing their contents and invalidating our evidence. When a file or data is "deleted" on a HDD it still remains even if overwritten, and can be detected and restored as it still exists in the sector and can be addressed. But what of the SSD?
Unlike the magnetic hard disk, which tries to keep blocks of a file as close to each other as possible; an SSD spreads the load across all the unused transistors in the drive randomly. This technique, known as wear-leveling, avoids consistently storing charge in the same group of transistors, which would make them wear out faster. The computer’s operating system is not aware of this process thanks to the SSD’s onboard controller card.
Today’s SSDs self-destroy court evidence through a process that can be called “self corrosion”. Garbage collection running as a background process in most modern SSDs will permanently erase data marked for deletion, removing it forever in a matter of minutes after the data has been marked for deletion. It is not possible to prevent garbage collection by moving the disk to another PC or attaching it to a write blocking device. The only way to prevent self-corrosion is physically detaching the disk controller from flash memory chips storing the data, and then accessing the chips directly via custom hardware.

A common misconception is that discarded blocks of an SSD drive are immediately erased. This is not usually the case. Instead, the way the TRIM command operates is considering the contents of discarded blocks as indeterminate (the "don't care" state) until the moment these blocks are physically erased by a separate background process, the garbage collector. In other words, the TRIM command does not erase the content of discarded blocks by itself. Instead, it adds them to a queue of pending blocks to be cleared by the garbage collector.