If there are no witnesses then nothing can be proved nor the charge can be pressed against you.
There might be other evidence though that he/she has left on the victim, like strains of hair, bruises that fits his/hers hand etc. Also if the victim's story is believable and his/hers isn't as in not being able to explain where she/he was at that moment, it can still be a conviction. There are a lot of details going into this and many times it's the details that helps a rape victim for instance since it's rare there are witnesses.
Yes, they can be charged with assault. They may even be charged as an adult.
He struck a 12 year old boy, although he wasn't charged for assault.
She could be charged with assault. As an adult, an assault against a minor is going to be pretty serious.
At most he can be charged with is failing to report a crime or misdemeanor
If it's determined not to be an accident, they could be charged with assault.
No, but the 23-year-old boyfriend can be charged with sexual assault.
By her age she IS a minor - if that specific charge is an enhanced penalty offense in your state (i.e.- it is a greater offense to assault a minor than it is to assault an adult) then the assaulter COULD be charged with that offense.
It depends need more story
Yes, assault laws apply regardless of age. If a 21-year-old hits a 15-year-old, the incident should be reported to the authorities who can investigate and determine the appropriate charges based on the circumstances.
yeahAdded: The person who struck the first blow is usually the one charged with the offense. However, a defense against the charge might be that they were in grave fear of being imminently assaulted themselves. You do not necessarily have to suffer the first blow, in order to invoke the right to self-protection.
Potentially the 16 year old boy would be charged with sexual assault or rape. They could face jail time, a fine, and be put on the child sex offenders list.
In the US they are required to provide an attorney. It will be a public defender and paid for by the state.