A police chief has said paying a child rapist £10,000 as part of an investigation into a grooming gang was the "right thing".
Northumbria Police's Steve Ashman said the information provided by the man led to the conviction of 17 men and a woman for abusing girls in Newcastle.
Charities have criticised the force for paying the criminal.
Mr Ashman told BBC News he was as "certain as I can be" that it was "morally" right.
"What we've ended up doing here is putting dangerous men behind bars and protecting vulnerable women and girls that we simply wouldn't have been able to do if we didn't have that jump off point we got [from the information]," he said.
Mr Ashman also dismissed claims that the informant, known as XY, was asked by police to take vulnerable girls to sex parties.
He said the claim made by XY was "100%" a lie and had been rejected by a judge.
Mr Ashman said: "We absolutely did not task him to go to parties with vulnerable women and girls.
"The use of the informant was principally about finding out who might be involved, the cars they were using, the addresses they were living at.
"This was a starting point, it never resulted in XY being exposed to offending."
'Crossed the line'
The informant had himself served a prison sentence for rape.
The last of four trials, spread across two years, ended on Wednesday and in total 18 people were convicted of sexual exploitation and drugs offences.
Those prosecuted were from the Bangladeshi, Pakistani, Indian, Iraqi, Iranian and Turkish communities and mainly British-born, with most living in the West End of Newcastle.
The court heard how vulnerable girls and women were abused at parties or "sessions" in Newcastle.
Northumbria Police asked a previously convicted child rapist if he could get them more information about the parties.
The NSPCC said that using him in this way was a decision that "crossed the line".
Jim Gamble, former head of the Child Exploitation and Online Protection Centre, said: "Personally, I can't envisage circumstances where I would have authorised payment to someone convicted of rape.
"I can't imagine how you could have control mechanisms in place with an informant of that type that you were going to task that would give reassurance that they still didn't represent a risk to young and vulnerable women."
The defendants were convicted of abusing girls who were plied with alcohol and drugs before being forced to have sex.
A court heard the vulnerable victims, some as young as 14, were exploited by a "cynical organisation".
Over the course of the four trials, 20 young women gave evidence covering a period from 2011 to 2014.
The 18 defendants and their convictions
- Mohammed Azram, 35, of Croydon Road, convicted of conspiracy to incite prostitution, sexual assault, supplying drugs to a victim
- Jahanghir Zaman, 43, of Hadrian Road, convicted of conspiracy to incite prostitution, rape, supplying drugs to a victim
- Nashir Uddin, 35, of Joan Street, convicted of conspiracy to incite prostitution, supplying drugs to a victim
- Saiful Islam, 34, of Strathmore Crescent, convicted of rape. Jailed for 10 years
- Mohammed Hassan Ali, 33, of Bentinck Street, convicted of sexual activity with a child, supplying drugs to a victim. Jailed for seven years
- Yasser Hussain, 27, of Canning Street, convicted of beating, possession of drugs. Jailed for two years
- Abdul Sabe, 40, of Dean House, convicted of conspiracy to incite prostitution, trafficking within the UK for sexual exploitation, drugs offences
- Habibur Rahim, 34, of Kenilworth Road, convicted of causing or inciting prostitution, drugs, sexual assault, trafficking within the UK for sexual exploitation
- Badrul Hussain, 37, of Drybeck Court, convicted of drug offences
- Mohibur Rahman, 44, of Northcote Street, pleaded guilty to conspiracy to incite prostitution, supplying drugs to a victim
- Abdulhamid Minoyee, 33, of Gainsborough Grove, convicted of rape, sexual assault, supply of drugs
- Carolann Gallon, 22, of Hareside Court, pleaded guilty to three counts of trafficking
- Monjour Choudhury, 33, of Phillip Place, convicted of conspiracy to incite prostitution, supplying drugs to a victim
- Prabhat Nelli, 33, of Sidney Grove, convicted of conspiracy to incite prostitution, supplying drugs to a victim
- Eisa Mousavi, 41, of Todds Nook, convicted of conspiracy to incite prostitution, rape, supplying drugs to a victim
- Taherul Alam, 32, of Normanton Terrace, convicted of conspiracy to incite prostitution, supplying drugs to a victim, attempted sexual assault
- Nadeem Aslam, 43, of Belle Grove West, convicted of supplying drugs to victims
- Redwan Siddquee, 32, of West Road, pleaded guilty to supply or offering to supply a class B drug. Jailed for 16 months
The police investigation, Operation Sanctuary, is continuing.
There have been about 100 convictions so far.