Williams has previous convictions for robbery and wounding
A robber who stole £84,000 of jewellery during violent attacks on wealthy women has been jailed indefinitely.
Devin Williams, 24, from Harlesden, north-west London, preyed on women, mainly young mothers, in Hampstead and up-market areas of London.
Williams carried out his attacks with up to four accomplices, most of whom are on the run, the court was told.
He pleaded guilty to five counts of robbery from May to August 2007 at London's Southwark Crown Court.
The court heard all five victims were grabbed from behind in a choke hold and wrestled to the ground.
Williams and his accomplices stole rings from their victims' fingers, ripped away earrings from their ears and tore away their necklaces.
One woman had her £32,000 diamond-studded engagement ring taken, which Williams sold soon afterwards to a jeweller.
By the time Williams had carried out his last attack he was under 24-hour surveillance and had teamed up with Jamie McKie.
The pair were caught and arrested when two teams of police officers watched as McKie approached a victim and pulled her to the pavement.
Williams, then moved in and stole her ring. It was found in Williams' mouth when he was searched.
McKie also admitted this attack.
Both men have previous convictions for violence, including robbery and wounding.
Passing sentence, Southwark Crown Court judge Stephen Robbins said: "Anyone who follows the news would have seen that there has been a startling increase in this type of pre-meditated violent robberies targeting women."
He told Williams that his case was "much worse" as one of the victims was nine months pregnant at the time she was attacked.
The judge told him he would have to serve a minimum of six years before he could be considered for release.
McKie, who was told he "had not yet reached the level of criminality of your co-defendant", was jailed for six years.