A diamond dealer who had committed fraud, in February, Which in turns

Meaning:
A fraud was committed by a diamond dealer in February-- The fraud has caused regulators to ban certain types of bank guarantees-that exporters use to get paid and as a result it has caused increased funding problems for exporters.

The first part of the sentence (when the fraud happened) is in past and since there is no other event which happened at the same time: a simple past tense should be used.
For the second part of the sentence since the effect of the fraud is still prevalent in present time: a present perfect tense should be used.

Now evaluating the answer choices:

A. A diamond dealer who had committed fraud, in February, Which in turns
Use of verb tense had committed is wrong - already mentioned in the preface.
Placement of which dosen't seems correct.
Hence 'A' is wrong.

B. Committing $2bn suspected fraud by a diamond dealer was
Use of verb-ing modifier committing is wrong here
Use of past verb tense was resulted is also wrong.(mentioned in the preface)
Hence 'B' is wrong.

C. The commitment of suspected fraud by a diamond dealer has
The meaning of the sentence changes in this one, as now it seems like the commitment has resulted in something whereas the original sentence says fraud has resulted in something.
Hence 'C' is wrong.

D. A $2bn suspected fraud by a diamond dealer in February has
Seems correct, let's hold on to it.

E. A suspected fraud, of $2bn, by a diamond dealer in February was
The use of the verb was is wrong here. (mentioned in the preface)
Hence 'E' is wrong.

Which leaves us to 'D' and hope its right.