Is it permissible to make use of clothes and belongings left behind by a deceased niece, knowing that their source was ill-gotten wealth?

Among the greatest sins is oppressing people. It is obligatory to return usurped or stolen clothing to its owners if they are known. Otherwise, it is obligatory to give them away as charity on their behalf or to spend their value on charitable causes. There is no sin in benefiting from them if you are in need.