I think I'm going to have to click the Report Abuse button on you. It is strictly forbidden on these threads to wait for more information before spouting your head off. How dare you post a reasoned and cautious response!
The serial killer may very well be a Muslim. Or he (she?) may be Christian, Jewish, Buddhist, Zoroastrian or a friggin fire worshipper for all we know. First they gotta catch the S.O.B. You worry about motives afterwards.
They are not going to catch him/them alive.
Starkweather didn't go looking to people to shoot, other than the intial shooting of family members that is. After that he shot whoever got in the way, or whoever they thought was in the way. One of the bodies was dumped about a 1/2 mile from where my brother lives now, although that was out in the country then. My Dad and a buddy had reported to the police that the gas station where the guy crossed paths with Charlie was deserted and wide open. The place is now, as then, the site of a typical "Stop and Rob", although typical then, and typical now are considerably different.
Whitman was a one incident deal too. These guys are preplaning (although Whitman did that too) and executing the plan over and over again. A totally different M.O., and very atypical for a nutcase, let alone two nutcases (assuming there are two, but apparently some evidence points in that direction).