Exactly. Now I'm not police or legal experts but SURELY if a police force has possession of a letter like this, then there are protocols and statutory obligations to report this to the relevant authorities even if they are abroad.
I'm not quite getting how this is somehow Meghans fault for not "kicking up a fuss" (as said on one thread) or chasing up what was happening. What's the point us having law enforcement agencies in place to protect us if somehow it's the responsibility of individuals to be checking up on them doing their job? Furthermore Meghan has no authority over the police and I highly doubt she would have been told what was going on in an investigation.
People have argued that because Thomas Markle didn't live in the UK, the Met didn't have to do anything but I still believe it should have been reported to the right authorities. In a not too dissimilar case, the man that was charged with the attempt rape and kidnap of Holly Wiiloughby initially came to the attention of an undercover US cop who then alerted the Met police. So they are evident channels that exist for the sharing of this information.