In a report to the North Wales Police Authority's Audit Committee, meeting today at St Asaph, HTCU manager Glesni Driver said the unit's backlog stood at nearly 60 cases in March 2010 with some awaiting examination for eight months.
"This caused issues for the force with regard to the progression of extremely serious cases and the welfare of HTCU staff was also of concern.
She said two issues relating to the case management system used by the HTCU remain to be resolved.
The system, called Fiasa, was developed by two former North Wales Police HTCU employees as there was no case management system available for the specific work of such units.
It has been continually updated for free by the developers as the North Wales Police HTCU is being used as a pilot to test its effectiveness.
"The compromise of relying on a Detective Constable's experience in this area appears to be working so far, but the HTCU is highly vulnerable if key members of staff were absent for a prolonged period," says the report.
It continues: "The HTCU's backlog of work is causing delays to criminal investigations and the poor quality of its management information means that it is largely unaware of the extent of the problem."