Durai to me just sounds like a hardcore criminal. We are also under the impression that the Mallers are ex-prisoners right?

To me he doesn't seem like ex-military except for his marksman skills. He attacked the Tower and got his ass completely handed to him. There is even mention in the corresponding chapter that says easy it is to defend, rather than attack and also another mention of vertical height advantage over your enemy. If Durai was some kind of wicked sick military person, you'd think he would have known this and attacked differently. Personally I would have just arrived in the night with a small crew and tossed Pipe bombs everywhere.