an accessory after the fact may be what you are looking for
a witness
It depends on whether they think the person is part of the crime as well. If they do, then the person is called an accomplice... someone who helped the suspect commit the crime. If not, then the person is just an associate... someone who knows the suspect and might be able to identify where he or she is.
If they were not in a competition, they should call the police. They have committed the crime of battery, which is illegal.
You can call a person who knows what they want assertive, decisive, or self-assured.
Dora or Jane or whatever you want to call her she is the person who stands by the door and is Emily's guardian.
There is no specific word for this.
A person who commits a crime is known as a criminal.
Depending on the circumstances, a person can be called an “accessory” to the crime, for harboring a fugitive. The person is an accessory to a crime if the person: Conceals or destroys evidence of the crime, or Harbors or conceals the person committing the crime.
vulcanologist.
a witness
you call them a computer tech
They are called the Coroner.