My thoughts exactly. These parents may be heartbroken but they do not intend to take any chances of PF getting away with the murder of their daughter. I agree, they are seeking witnesses - and more proof with these actions - they are effectively tightening the noose around PF’s throat.
It is also abundantly clear that KB was her parents daughter - same determination, intelligence and strength. It makes me very emotional to think about the amazing strength it took them to set aside their grief and pursue their own justice.