"I offer my sincerest thanks to you for your leadership, and to your colleagues for their diligence and persistence."
I am writing to express my appreciation for the work done by you and your team in service of [victim], her family and friends, her community, her country, and our society at large.
So many things had to be done well; so many tasks carefully done, to bring justice. I salute you, and every person who put their hand to this case, right down to file room folks, the mailroom staff, and the many administrative people who completed their work carefully and thoroughly over a stretch of decades.
I offer my sincerest thanks to you for your leadership, and to your colleagues for their diligence and persistence.