A health trust has offered its "sincere apologies" to the relatives of people whose organs and tissue samples were kept without their families' knowledge.
At least 13 samples, taken from post-mortem examinations after unexplained deaths, were found during an audit at South Tyneside District Hospital.
South Tyneside NHS Foundation Trust is investigating the circumstances of the storage which came to light in 2015.
Northumbria and Cleveland police forces are also involved in the inquiry.
'Upset and angst'
Ken Bremner, the trust's chief executive, said: "I want to express my sincere apologies to all the families involved for the distress and anxiety that this will, undoubtedly, have caused.
"A review of this nature, covering a time period that goes back over a number of years, will, unfortunately, take some time to conclude."
He said the trust was working closely with police, the relevant coroner's office and the Human Tissue Authority.
Northumbria Police said: "This is understandably an incredibly emotive issue and we recognise it has caused a huge amount of upset and angst to those involved.
"It is with regret that the samples were not identified sooner and this is a matter that ourselves and the hospital have taken incredibly seriously."