I think Shariah permits summary execution in this case. And also when it happens, does the Islamic state punishes the murderers at all ? I think mostly they don't even try to catch the perps.
No Sharia law is very strict on murder and rape. A fine must be paid, meaning the murder/rapist actually has to do some work, unless he owns an oil field. Also, if he rapes someone and they are wounded for life, he owns her now and must take care of her. So by strict I mean to the victims, not the aggressor.