why is DNA itself is not a core Shar’ee ground for conviction for crimes?

  The Shar'i requirements for the execution of corporeal punishment (hadd) has expressly been mentioned in the legal sources of our shari'ah.viz,admission of guilt or the testimony of four witnesses.
  The establishment of a biological relationship between the child and a strange man (to the mother) is not grounds for the shari' consequences to come into effect. In an authentic hadith nabi (saw) mentions that the child (i.e his lineage) belongs to the man in whose nikah his mother is and the one guilty of zina is deprived. Here, the establishment of a biological relationship between the child and the fornicator did not bring about the shari consequences of parenthood. Similarly,the establishment of a biological relationship between a child and a strange man (to his mother) do not bring about the shari consequences of corporeal punishment.
  Secondly, the object of admission of guilt and the testimony of 4 witnesses is not the conclusiveness of the evidence. Had thus been the case then evidence presented by DNA analysis may also be rejected due to the results being prone to a margin of error albeit minimal.
  Allah (swt) is the sole legislator of this deen and the execution of punishment is primarily His sole prerogative. Those guilty of breaking his commandments will be answerable to Him directly in the hereafter and will have to bear his wrath. As a secondary measure Allah (swt) has set out the requirements for the execution of punishment in this world.The rationale behind these requirements is known to Him .If these requirements are not found ,alternate means will not be adopted.Rather,the matter will resort to its primary position (i.e accountabilitry to Allah(swt). 

And Allah Ta'ala knows best.  

Mufti Imran Hatia
Student

Checked and Approved
Mufti Ebrahim Desai