No Muslim here has yet condemned it, which seems rather strange to me. Should I assume that some Muslims condone this kind of thing?
Of course some Muslims would condone violence and some don't. Just like SOME Christians, Buddhists Jews, Hindu, Pagan religious groups, ect. would condone violence but not all. Really, most Muslims don't do this or condone this. I already know this because I personally know Muslims in my life. I know there is good and evil in all of these groups, Muslim and Non-Muslim alike.
Remember there's a billion Muslims, they all don't share the same beliefs, rules, customs ect. Some groups will be more extreme than others, but it's naïve to assume hundreds of millions of Muslims would commit or condone terrorist activities. Especially when Muslim majority countries like Chad, Nigeria, United Arab Emirates, Jordan, ect. are actively FIGHTING against Islamic terrorist groups like Boko Haram and ISIS. So really, what more proof do you need?