Were the witnesses all the same nationality as one of the two that was arrested?
Happens every day, but that's the reality of life witness testify and are trusted.
Case in point. I got into an accident with a Spanish driver in a predominantly Spanish neighborhood. Other driver hit me when my car wasn't moving going approximately 30 miles over the speed limit 60 in a 30. Totaled a brand new van. Spanish cop shows up and conducts a conversation in Spanish with the other drivers, asks bystanders in Spanish if they saw what happened, after all this is done he takes my statement in English. He writes me an at fault accident report. Asked for his supervisor and she showed up quite mad, and backed him saying he followed protocol, and asked witnesses. These stories go both ways, and trust me it sucks when you are the one taking a hit in a clearly biased situation. Not to mention that this is the USA and at the very least all conversations should be in English. He did what he did and technically followed protocol so I did not pursue it with the cops. I did make my case to insurance though, but that is a story for a different time.