I fail to see what they did wrong, even in hindsight.
Firstly, they did not notice a 777 flying over their territory on their radar systems.
Secondly, when they found out that a plane had crashed and scrutinized their air defense systems, it took them days (and many re-re-re-statements) before they acknowledged that a 777 had crossed their country without anybody noticing.
Finally, it took them at least two days to take the data from Inmarsat seriously, that stated that the plane had flown for another 5 hours at least.
All this meant delays in the search operation, which means wasted resources, and above all: TIME. The chances of finding anything in an ocean full of currents and winds don't get any better when you wait (waste) a couple of days.