I believe in abortion. But I don't like that argument. Because the easy counterargument is, "It's not her body, it's the baby's body." So, if you commit murder, it kinda is other peoples' business.
At the same time, the same argument could be used loosely to justify killing your child. "He's a part of me, so I can do what I want."
In other words, at what point does the baby's body become his or her own and not the mothers'? By your argument, basically not until birth--it could be used for, as the baby is still technically connected and part of her until the cord is cut.
I'd prefer to address the "abortion is murder" aspect, first.