How long is a detanier help on a person that violated probation?

my friend was accused of something he did not do he had his arm around his girlfriend and the cops rode up screaming at him telling him to get off of her and dat he had her in a head lock because she was crying she was crying that happened and he was trying to calm her down now what makes it worst was he's on probation and they locked him up because they clam they saw something when his girlfriend said she was fine she didn't want him locked up and she even went to go make a statement and she didn't press charges now in jail for something he didn't even do with a case of domestic violence/headlock so can someone please help me understand whats going on because this is the most stupidest case i ever heard i live in philadelphia pa and there's been so many killings its ridiculous that they can't find the people doing all of these shootings but can lock people up for headlocks or what they think they saw...