According to ESA Sentinel1 satellite image, an oil slick in the search area was found at 33°32' N / 29°13' E – about 40 km southeast of the last known location of the aircraft. And that information relayed to the search authorities.
A0283 note - Sentinel1 is one of a series of satellites of the ESA Sentinel series. There is an 1a and a 1b. Most likely this is from 1a (the older one). Claiming that the slick is from the aircraft is very very premature.