mosley was on the clear and holyfield introduced boxing to steroids. because you cant go from a crusierweight to heavyweight in 1 year adding 10 to 15kg naturally with his training. 
plus he hired lee haney for training so i wouldnt be surprised if he gave him a few pointers
You are misinformed about Holyfield.
1. He never put on 10-15kg (22-33lbs) in one year. Ever.
2. His last fight at Cruiser was in April '88. He weighed in at 190lbs. By this point in his career he was consuming less calories than before to make weight. His first fight at heavyweight was in 3 months later (July), and he weighed 202lbs.
His next fight, he weighed 210, then he weighed 208, 207, 212...... The most he ever weighed was 221, (year 2000). His preferred fighting weight was less than this. Infact he only weighed 214 in his last fight in December, and that was at the grand old age of 46!!
I think the whole "steroids thing" came because of the shape of his muscles, namely his impressive chest and traps. Bottom line, Holyfield was/is a tiny heavyweight, and suggesting that 'Holyfield introduced boxing to steroids' is a disgusting and hideous claim.