Ten policemen have gone on trial in Brazil, accused of murdering twenty-one people in a Rio de Janeiro shanty town in 1993.

Prosecutors say it was a revenge attack by the police officers after four of their colleagues were killed by drug traffickers from the shanty town.

The trial was suspended earlier this year after the judge disqualified a key prosecution witness.

Some forty other officers are also awaiting trial, accused of involvement in the killings.

Human rights groups say the case is likely to highlight the links between some members of the police force and drug-traffickers.