Firing upon coming off of Doctor recommended leave

My husband was hired for a non-union company that employs over 500 people on 3/10/03.
Here are the facts:
3/10/03--Hired as JR. Paint Process Engineer
8/25/03--received 2 letters of recognition for outstanding performance
8/28/03--received written warning for programming wrong pathword to robot (however they did not follow the employee handbook by giving a consaul, or verbal first), also supervisor did exact same thing 2 weeks later and received no kind of discipline.
9/12/03--received probationary review and was given very good remarks
9/18/03--received 2 more letters of recognition for outstanding work
Late Oct '03--took a vacation day for wife's outpatient surgery
11/10/03--started a one week vacation due to wife's major surgery
11/14/03--received a letter of recognition for outstanding work
Late Nov.'03--was told would HAVE to go to 2nd shift starting Jan. 5 '04 (didnt like it, argued some, but did it anyway)
01/13/04--went to doctor for abdominal pain, was sent to ER. ER docs wrote off work for 2 days.
01/15/04--was asked to come to work early so yearly review could be done (they knew he was still ill). Supervisors gave poor review but with the understanding that improvements would be worked upon. He disagreed and signed the review under protest. Only worked 1/2 the day because of pain, doctor wrote him off until Jan. 20th.
1/20/04--saw doctor, was written off work until the 26th, due to Intestinal Bacterial Infection.
1/26/04--came into work, was fired.

They say it was because of his "poor performance". How could that be with all the letters of recognition? He took it to the company headquarters for "Employee Fair Treatment" and they were told that the company said "He's a great person, good worker, just wasnt what we were looking for." They did ok him for unemployment. Upon his firing they told him "You will be short on your check". He was a salary employee. They only paid him for his days worked which equaled out to be about 2 1/2 days for a 2 week period. Shouldn't he have received his full 2 weeks? Before he took the time off (advised by his doctor) the HR people told him that it would effect his pay. They suggested we file for short term disability but because he had worked 2 days that week that he would not qualify for it. Therefor they suggested he use one of his vacation weeks. Since it was a new year, he had new vacation time. He did inquire about it, but a few days later is when he went back to work, and they fired him before ok'ing the vacation.
Also, when they fired him they gave him nothing in writing stating why. It took us over a week and some pressure from un-employment, welfare, and the Fair Treatment People that this company finally gave him in writing their reason. It states: "review indicates that your ability to meet the expectations of the position for which you were hired to perform have decreased." Huh? Then why the letter of recognition in Nov?? Also it says: "you received a verbal warning and a written warning for performance in less than one year of employment. Your employment progress seems to be going in the wrong direction." He NEVER received a verbal warning (was never documented in his file) and according to employee handbook they go under something called CAP (Corrective Action Program)and it oulines the following guidlines and states: CAP,is for providing an employee with sufficient notice of a performance problem and ample time to correct the problems to meet expectations. Upon successful completion of your probationary peried, you are elegible for corrective action under the CAP system. (which he was) 1.Counseling: which is to be documented in employee's file (he never received)2. Verbal: should be signed and documented into employee's file (never happend) 3. Written: to be signed and documented (only thing he ever received on 8/28/03)
4.Suspension: length of time depends, upon returning bring a letter stating how you intend to improve, a formal letter will be drafted and signed by employee and supervisor's (never happend) 5. Termination

He was hired in as a full time employee under a contract but no significant time period is stated. Also, I do not see anywhere in the contract about "at will" on either part of the company or employee. Nor do I see this in the Employee Handbook anywhere. Does my husband have any type of legal recourse?