The software that will do everything you mentioned is called "Cool Edit" (It may have a new name now that Adobe has bought it)
With my cheapo music keyboard I can. become a complete orchestra.
Needless to say,someone well acquainted with it can do a lot more.
Audio of any kind should NEVER be accepted as evidence.
Adobe Audition, I use it every day at work. Just goofing around one time a few years ago, I took a recording of a single gun shot and edited it to make it sound like 50 men were firing multiple shots at each other.