First things first, the police will need to try and identify the attacker. As the attack was from behind and your husband was knocked out after the first hit, I am assuming he would not recognise the attacker again. Therefore police will have to make enquiries such as CCTV, nearby residents etc.
If they cannot identify the attacker or have no witnesses/CCTV - there will be nothing they can do, because they cannot arrest anybody.
If they do know who did it, they will take a statement from your partner. They will then interview the attacker.
From the interview the police will submit a file for review. This can be by a senior police officer and/or CPS solicitor - they will then decide from the evidence and the interview what is the most appropriate action.
If you would like to know more...let me know what the police have told you so far and I can tell you the process from there!