Look at the CD jacket and find out who the songwriter is. It doesn't matter if the songwriter is in the band or not; the songwriter owns all intellectual copyright to each song he writes, the minute he writes it, no paperwork needed.
Look for the copyright symbol. Once the song has been written down on paper and recorded, it is eligible to be registered. The person, company or band listed after the copyright symbol owns the rights to the song and usually is the one who gets the money from it.
Look for "Recorded at..." on the CD jacket. Following is usually the name of the studio where the song was recorded. This studio owns the rights to the song if it is sampled, covered by another band or becomes part of a compilation album.
Check for any names of publishers. If there is a publisher listed, that publisher owns the mechanical rights to the song. If there is no publisher listed, then the band or record label owns the mechanical rights.
Search for the record company on the Internet. Find the band on the company's website and check to see who helped compile the album or song. If the band involves any outside people in writing or arranging their song, then those people partially own the song and are usually given co-writer's rights.