This is more apt to encourage an honest testimony on their part, fearing that their oath may be disregarded like that of the previous witnesses. You shall observe God and listen. God does not guide the wicked.
ذٰلِكَ أَدنىٰ أَن يَأتوا بِالشَّهٰدَةِ عَلىٰ وَجهِها أَو يَخافوا أَن تُرَدَّ أَيمٰنٌ بَعدَ أَيمٰنِهِم وَاتَّقُوا اللَّهَ وَاسمَعوا وَاللَّهُ لا يَهدِى القَومَ الفٰسِقينَ
zaalika adnaaa ai ya’too bishshahaadati ‘alaa wajhihaaa aw yakhaafooo an turadda aimaanum ba’da aimaanihim; wattaqul laaha wasma’oo; wallaahu laa yahdil qawmal faasiqeen