The swearing on the Koran is an interesting issue since apparently it is OK in their religion to lie to the infidels.
That's my understanding, too.
It's not really a way to avoid a perjury charge. You can't come back and say "I didn't really mean it" after swearing an oath to tell the truth.
Witnesses will lie or they'll tell the truth. The presence or absence of any holy book will not change that.