The US Justice Department is considering revoking years-old settlements to open fresh probes into banks alleged to have rigged interest rates.According to sources cited by Bloomberg, prosecutors could decide to scrape the agreements with each lenders, if they're found guilty of having committed crimes after the settlements were negotiated.In recent years, the US Justice Department has often utilised so-called deferred prosecution and non-prosecution agreements, a measure which is often described as placing banks "on probation".Under the deals, which have been criticised in some quarters as being "overused", banks are required to admit responsibility for any wrongdoing and cooperate with the investigations.However, should prosecutors decide to revoke the settlements, which would be an unprecedented move, lenders would be subject to criminal charges.Barclays, UBS Group and Royal Bank of Scotland have all subscribed to similar agreements to settle investigation into rigging the Libor rate, while along with JP Morgan and Citigroup they were negotiating with US authorities to resolve currency-rigging allegations."The Justice Department now understands that these deferred-prosecution agreements don't always work and there have to be serious consequences if companies don't take them seriously," Brandon Garret, a law professor at the University of Virginia was quoted as saying by Bloomberg.