Now, we have no way of knowing exactly what happened. The girl says one thing, the prosecutor believes another. He probably believes something happened because either 1) the girl at one point said there was (she may have been lying at the time), 2) there is some physical evidence (think Monica Lewinsky's blue dress), 3) there is a witness (who may be lying), or 4) there may be a hearsay witness (who may be lying).
Damn, I should've read the freakin' article more closely. It says:
Sanchez-Pesantes is accused of unlawful sexual conduct with a minor stemming from a Jan. 20 incident in which the boyfriend of the girl's mother allegedly saw the two on a couch. The girl denied having sex and refused to write a statement for police, defense attorneys said.
There you have it:
A witness either saw something illegal, thinks he saw something illegal, or lied and said he saw something illegal. To complicate matters, if the man told the girl's mother, many girls would be afraid of getting into trouble and immediately deny anything that mom would disapprove of happened. Once either party (the man or the girl) lies or says something happened when they were mistaken, it becomes very difficult for them to change their story without losing credibility.
This is a classic he-said/she-said. Rather than look for other evidence, it looks like Mom and the cops are simply trying to eliminate the "she-said" and proceed with a conviction.
Sounds like the Akron police have Gitmo Envy.