On when voluntariness of confessional statement can be challenged and whether confessional statement alone can ground conviction:

It is at the trial-within-trial that an accused person can effectively challenge the prosecutor as to the voluntariness of a confessional statement. If the confessional statement is admitted after the trial-within-trial the accused person cannot argue that he did not make the confession voluntarily without first impugning the trial-within-trial. A voluntary confession which is direct, positive, and satisfactorily proved is sufficient to warrant conviction even without any corroborative evidence so long as the court is satisfied of the truth of the confession.

JOSEPH AKENKULE SALE v THE STATE – SC. 635/2016 decided on 5^TH JULY 2019