John Walker Lindh is a troubled loner who had a hard time fitting in. As is Richard Reid. As is the Aussie convert in Guantanamo. As is that idiot in Maine.
White converts to Islam are, as a general rule, troubled loners.
Additionally, his father's denials are particularly hollow.
If his son was capable of blowing himself to bits like this, he was capable of converting to a religion which encourages such behavior.
I suspect that when he converted to Islam, the last person he would have told about it was his father.