It is worth keeping in mind that "beyond reasonable doubt" is NOT "beyond a shadow of a doubt". The narrative either adds up to a cohesive, believable sequence of events or it doesn't.
Either: Allison's cheating husband, facing financial ruin and under pressure from his mistress to end his marriage once and for all, killed his heavily insured wife (and am I right in thinking her death occurred on the last day she was covered by a policy they couldn't afford to renew?), transported her body in the car where blood was later found, and dumped her off a bridge
Or
Allison killed herself, via an unknown/undetectable mechanism, in a location she was either transported to by unknown means/person(s) who haven't come forward, or she walked to in the dark for in excess of two hours...
Or
Allison was killed by an unknown person who didn't rob or rape her...
And Gerard's facial abrasions were genuinely caused by a razor even though experts find that highly improbable...
And she coincidentally picked up botanical traces that match the low growth around her house...
And the blood came to be there by innocent means in the brief time she'd owned the car...
The question isn't: is it possible to find another explanation for each individual piece of information? The question is: taken as a whole, is it reasonable to conclude the prosecution's case is the most likely explanation? Is it reasonable to believe it was a series of increasingly unlikely coincidences - he just so happens to self inflict unusual shaving cuts on the very day his wife was killed in a random attack by a stranger, which is a very unusual murder (see: Jill Meagher), which coincidentally happened as his self-imposed deadline approached to leave his wife, etc.
I believe a reasonable person would be required to accept far too much happenstance to conclude he was innocent. Any alternate scenarios I can think of require too much of the fantastical to seriously challenge the simple explanation: the man with means, motive and circumstantial evidence pointing to him is the one who did it.