How to handle a company you are contracted through with they fire you under false reasonings

The employer my spouse works for contracted him to another employer. Last week there was an incident when a fire alarm went off. He was then inform to contact the fire dept and later instructed to dis regard the call by a person of the company he is contract through. Along with that another employee of that company reset the alarm system which is against company policy and this alarm system can only be reset by the fire department. When higher ups asked who reset the system the guy never admitted to it and the tape was pulled with them seeing that he pulled the tape. Later my husband was asked to give a written report on the incident which he did and it included information on being instructed to disregard the fire dept call and the person who reset the system. The statement he gave was later changed by someone in the company and that important information was taken out after the president of the company stated he wanted a investigation conducted. My husband as well as all other employees were trained on the system again. He receives a call on Friday from the company he actually works for stating to leave his badge and come in on Monday to discuss what has been happening. In a 3 day period the company he was contracted through have made statements about events never happened just to try to justify why they wanted to get rid of him only after the company he works for stated they needed to provide a reason. He has never been written up and the contracted company has only complained about him once ( when he missed work because of a toothache and documentation was provided from the ER for him to be off). My spouse believes that this is defamation of his character because they had to falsify information about him to get rid of him so that information regarding the alarm incident was not exposed to the president of the company. The company that he actually works for stated that because of the reasoning they provided this might prevent him from receiving employment at the same equal pay that he was getting because a question may arise as to why he was let go. He has been accused of coming in to work late ( tapes can be pulled to prove otherwise as well the many compliments and thanks from the contracted company about his punctuality to later say he is always late),