science20.com – NASA have put a great deal of work into the engineering for a sample return but I can't find any papers or blog posts or any sign of prepration for the legal side of the return mission. We are strongly protected by many environmental laws and laws to protect human health that we didn’t have at the time of Apollo.

Source: F. Javier Martín-Torres, et al. Transient liquid water and water activity at Gale crater on Mars. Nature Geoscience, 2015.