The Chief Constable who led the report that found a secret Scotland Yard unit held information on families of 17 justice campaigns admitted it would be "distressing" for relatives to learn that their details were being held.
Mick Creedon, Derbyshire Chief Constable, added that it "must seem inexplicable" for the families who have had their details held by the force.
One reference in the report was to an unnamed individual planning to go to a funeral, even though "there was no intelligence to indicate that the funeral would have been anything other than a dignified event".
Mr Creedon said: "Unless the information could have prevented crime or disorder it should not have been retained."
Despite the report finding no evidence that covert operations targeted grieving families, the fact information that had no relevance in preventing crimes was kept, was heavily criticised.
More top news
Murder charges against an Irish nanny, who spent more than two years in prison accused of killing a baby in the USA, have been dropped.
Charities face probe after claims they may have been involved in buying and selling widower's details.
The island of Kivalina in Alaska is quickly disappearing into the ocean, watched by its 400 residents, due to climate change.