It was reported that he had been depressed following the death of three of his Congressional aides in a 1972 car accident, and by the fact that his mentor and predecessor, Rogers Morton, was suffering from cancer. However, five days before his death, it was revealed that Mills had received an undisclosed $25,000 gift from the finance committee of President Richard Nixon's re-election campaign during the 1971 special election. Overall, it was part of $900,000 in unaccounted donations made by the committee, according to the General Accounting Office. If Mills were convicted of conducting illegal activity, he could have faced a $1,000 fine and one year in prison.