The comment was made as Mr Justice Ronald Weatherup prepared to set a minimum jail term at Belfast Crown Court for the murder of a schoolgirl 30 years ago.
Black, 64, was found guilty last month of snatching Jennifer Cardy as she cycled to a friend's house in Ballinderry, County Antrim, in 1981.
He then dumped her body in water close to the main Belfast-Dublin road near Hillsborough, Co Antrim.
As lawyers offered arguments around the length of prison term, defence barrister David Spens said: "This is one of those rare cases in which there is no mitigation and so I propose to say nothing in that regard."
Prosecution barrister Toby Hedworth QC argued that killings subsequently carried out by the former delivery driver should be taken into consideration.
"This is a man who has committed four murders rather than three murders or one murder," he said.
Black was in Northern Ireland on a work trip from London and caught a ferry home after killing his nine-year-old victim.
He is already serving multiple life sentences in Wakefield prison.
Jennifer's murder was the fourth for which he has been convicted.
In 1994, he was found guilty of three unsolved child murders in the 1980s - those of 11-year-old Susan Maxwell, from the Scottish Borders, five-year-old Caroline Hogg, from Edinburgh, and Sarah Harper, 10, from Morley, near Leeds.
Mr Hedworth argued that Black should face a whole life term, given his other killings.
He said jail terms set in 1994 would have been higher had his other crimes been known.
Jennifer's family were in court today to see the killer sentenced.
Defence lawyer David Spens QC argued in favour of a discretionary sentence for the murder of the Northern Ireland schoolgirl.
Following a six-week trial, the jury at Armagh Crown Court delivered unanimous guilty verdicts on the counts of kidnap and murder after deliberating for four hours and 15 minutes.
Detectives in England are reviewing the evidence against Black in connection with another schoolgirl's disappearance.