I don't mean any disrespect here, but it's possible you missed something? It happens to me all the time with Black Mirror since it can be a deep show, and in the case of Crocodile, the episode felt like it had ended sooner than it did (I very nearly skipped to the next episode thinking it was over before the last two scenes and I wonder if that's what you did because that's where the guinea pig info was). Here's what happened:
The lead detective at the scene of the crime says to an officer "I don't have any idea who we're looking for, but it's a good thing you're not asking me." She nods at the guinea pig. "Now let's get out of here and let the recall team do their work." They show cops powering up the memory device right next to the guinea pig's cage and they take it out of the cage. Then there's a cut to the police showing up at the recital where Mia is and someone pointing out to the police where Mia is sitting.
If the show didn't want to lead us to the assumption that the GP's memories led them to Mia then why put this as the ending of the episode?