Crucial Support of a Girlfriend - Puzzle

A man escapes from jail with help from his girlfriend. Four girls are accused of being the man's girlfriend. His girlfriend is lying. Two girls are innocent and telling the truth. The other girl is the man's sister who is helping the girlfriend lie. 

Who is the man's sister?

Amanda: "Melinda is his girlfriend."

Vanessa: "Eva is lying."

Eva: "Amanda is lying."

Melinda: "Vanessa is not his sister."

Know who is man's sister!