First rule of leadership is: Leader is guilty for everything.
My rule for it is: it's all about Trust. Mutual.
Are u a real Leader? Then stick with them. Work together. Do their shifts/stuff if they cannot come in the afternoon. Let them take your shifts/stuff when u cannot do it. Share living and working, together. And all this under pressure. Long-enough to start knowing who thinks of what and how, when s/he says this or that. Or when s/he writes such and such code. The saying goes like - Eat a 10kilo of salt together... By that time u'll have a feeling about everyone, who is able of what and unable of what, how fast s/he thinks/learns/find/a-way-out, how persistent s/he is in chazing a defect/completeness/perfection, and all those. As bonus, u may become friends. For life. Anyway, here's my take on work/teaming/trust etc http://www.svilendobrev.com/rabota/doverie.html and around