It's always best to not speculate but wait from a report from the NTSB. From my point of view the aircraft was roughly 800-1200 ft in the air when the engine sputtered and within 15 seconds was in the water. It entered while in a spin, nose down, around 100-120kts. I'm unsure why/how the aircraft entered the spin, I've several hundred in various aircraft. It did appear the pilot was trying to pull the aircraft out of the spin prior to impact. There was significant debris.

"Castastrophic Failure" is when a really vital system on the
fallen aircraft happens in a tragedy as this.
Failure of the mechanic(s) from the hanger which are
the one giving the all clear to fly said aircraft.
Hopefully not a criminal element involved.