Proof of employment, community service, solid character reference letters, a sincere letter from your husband offering insight into past bad behavior .... These are a few items I think the board will want to see. Under no circumstances should he attempt to blame anyone else for the circumstances leading to a prior conviction-- if he can afford to hire an attorney to help present his case he should certainly do so. Good luck.
The response I have provided is general in nature, and does not create an attorney-client relationship. My practice is based in Rhode Island, and the law and practice in other states or jurisdictions may be different.
The manner of life he has led since his conviction; employment history, community service, acceptance of responsibility along with a statement of contrition. It is not an easy process, and depending upon the nature of the charges an applicant, while eligible to apply, may not be granted a pardon the first time. You should contact an attorney who handles these matters to assist in the application process.