Interesting theory. If Litveninko was trying to hide his Islamic ties, why the death bed conversion ? It only weakens his credibility. He may have simply been making one last statement. One last slap to Putin's face. Yes I know the pro-Putin theory is that he waited until the end when the effect would not be great, but doing the conversion when the whole world was watching him die, gave it as great an effect as it ever could have.
The last minute conversion to me indicated mental instability and enforces the suicide theory.