I think my aunt was killed...?

My aunt was found dead at 53 on 10-11-06 @ 6:30 am by her husband. It was ruled she had a heart attack. But received a bill of good health the morn she died. 5 days b4 she died her daughter said her step-dad beat her so bad she could not get out of bed 4 the 5 days. the morn she was found my uncle said he woke up and went 2 do his normal routine. He then gave my cousin the keys 2 her moms jeep & told her 2 take it 2 work & lock keys in the jeep. He walked her outside, 2 make sure she got in and left. My aunt always took her 2 work so why was this day dif. My mom went over & found my aunt laying in the fetal possition & her body was now a blk color. My mom noticed the pillow on the bed had some black stuff on it. Through out this all there has been several stories told by my uncle about how he found her. We think he smoothered her 2 death. Why did her body turn blk? What can we do? Please give me some good advise. Its killing the family.