Flat roof leakage

[roof_leakage]

My parents had their flat-roof fiber-glassed over the summer. Fiberglass was applied over existing roof. Contractors drilled into the existing roof to fit the battens. The window was also replaced. When it rained the roof started leaking - small leak at first (above the window). The leak is getting worse as the weather turns. Now water is dripping from the top of the window (window sil?). Recently leak marks can be seen in the middle of the room ceiling (2nd picture). The source of the leak is still un-known, but it only started after the works were done.

The contractor hasn't been of much use (he denies it is the roof, initially claimed it is the drain pipe). He came to look at it twice over a 3-4 week period, but is not picking up phone calls anymore.

Leak above the window (all the cracks started appearing after the leak)

This week the ceiling started showing sigh of leak (window from 1st pic at the end)

roof

Is there any way to figure out where the leak is coming from? What kind of specialist can we use to identify the leak and fix the issue (hopefully avoiding the cow-boy builders like we had)

We have applied one coat of Acrypol+ Grey Waterproof Roof Coating yesterday (not sure if this will help)

 

[catlad]

There appears to be rather a large gap by the side of the cill in the last picture!