1) When the ALCU tested mugshot photos VS congress member photos, the ALCU set it to use an 80% confidence level threshold, which should result in a 5% false positive rate. There are 535 members of congress, which from this setting should have resulted in 26.75 misidentifications. The ALCU got 28 misidentifications, which is pretty darn close.
2) The ALCU use a comparatively small dataset of photos. Using a different, 30x bigger dataset, and a 99% confidence level resulted in no misidentifications.
3) The police are only supposed to be using this system to narrow down choices, and then have a human sorting out possible matches, which this should do very well.
---
My thoughts: The system appears to be functioning exactly according to specifications. The eternal problem of systems is that the specifications do not match what users are actually expecting/needing the system to do. If the ALCU is confused about how it works, the police probably will be as well.