Four former traders who worked for Barclays PLC BARC, -8.59% BCS, -3.27% have been sentenced to prison for conspiring to illegally fix global benchmark interest rates, news reports said Thursday. The sentences, ranging from 33 months to six-and-a-half years, were handed down by a judge in London. Jay Merchant, a 45-year-old former derivatives trader, received the longest sentence. The four men will serve half of their sentences in prison and then be released on parole, said Judge Anthony Leonard, according to a Reuters report. The men were accused of trying to fraudulently influence the London interbank offered rate, or Libor. That benchmark is used to set interest rates on trillions of dollars in financial contracts. The U.K.'s Serious Fraud Office is seeking a retrial of two former Barclays employees charged alongside three of those sentenced, after a jury earlier failed to reach verdicts for the pair.