He might well have been considered as a murder suspect. I don't know that as a fact, however because I am not an investigator with access to case files.
I do know how evidence rules are supposed to be applied at trial. Often investigators know who committed a particular crime, but lack the necessary admissible evidence to charge the person.
A previous conviction cannot be mentioned at trial, nor can any misconduct not charged - unless it can be directly linked to the charges being heard. During sentencing, prior convictions can be mentioned, but with caution.
At Fred Coffey's 1987 murder trial, he was found guilty of brutally killing a little 10 year old girl in 1979. During the sentencing phase, it was brought up that he had previous convictions on 9 counts of child molestation which occurred in 1986. He was sentenced to death.
He appealed the sentence, stating that he had been unfairly predjudiced by introducing the child molestation convictions. The appellate court AGREED with Coffey, on the convoluted reasoning that although he had been convicted of the 1979 murder, his molestation of 3 other children 7 years later did not bear on the murder. And he might have become a child molester AFTER he murdered the little girl.
As a result, Coffey was given another trial and all reference to other convictions were excluded from consideration. At that trial, it was a 10 to 2 jury vote for the death penalty, but without a unanimous vote, his sentence was commuted to life, and he was eligible immediately for parole! Thankfully, he has remained in prison, but comes before a North Carolina parole board periodically.
Although only convicted of one murder, Coffey is a prime suspect in several others as well.