My question involves civil rights in the State of: Illinois
I would like to know if it is legal if a person happens to record a passerby with a cell phone camera who threatens them on a public street. The camera was already on, as this person habitually turns it on when they begin their walks and turns it off afterward. On this occasion, however, another person turns around and follows them and points a can of mace at them, telling them to stay out of their way. The person with the camera says nothing to the other person and, not wanting to have a confrontation, keeps walking, ignoring the other person until they go away. The other person has not noticed that he has been recorded, as it is not done in an obvious way.
Have the rights of the threatening person been violated by being recorded in this (hypothetical) situation. I understand that Illinois is a two party consent state but, does he have an expectation of privacy here? Does the fact that he is committing a crime make an exception?
If the victim of the threat goes to the police with this video and files a complaint, can it be used as evidence against the offender? What are the chances that the police will charge the victim himself with illegal wiretapping or some other violation?

Thank you for your time.