Doubtful and Mixed Capital in Islamic Financial Institutions

One of the most controversed issues in Islamic finance is around the initial capital of Islamic banks and takaful companies, especially when initiated by a conventional parent company.
Some people doubt the purity of the capital in Islamic banks and takaful companies and as therefor question whether these organisations are truly Islamic when their capital is not completely halal.
There are two points to be made in relation to this problem:
1. Money itself is not unlawful, but becomes prohibited through the way it is procured, if it's not in line with the Shari’ah law. Sin does not move with the money from one party to another.
2. Capital earned by the parent companies of Islamic banks may not be all from prohibited businesses. Part of the capital is supplied from individuals and permissible government and private organisations, therefore, it is possible that the funds arised only from permitted sources even if combined with prohibited income.