A man convicted of plotting to steal around $338 million worth of diamonds in London launched an appeal Monday alleging the judge at his trial fell asleep several times, The Associated Press reports.

Raymond Betson, 41, was one of five men jailed last year after a meticulously planned robbery attempt at the Millennium Dome was foiled by a police trap. A sixth suspect died before he could be tried.

Police had been watching the gang for months and arrested the men as they attempted to smash through an armored glass display case with a sledgehammer on Nov. 7, 2000.

Betson’s lawyers said in court Monday they were trying to trace two witnesses who may be able to give evidence about when Judge Michael Coombe dozed off, the AP reports.

“Statements I have seen suggest that the learned judge fell asleep not just during a closing speech, but also during the evidence,” Betson’s lawyer, Edmund Romilly, reportedly said.

But Lord Justice Rose reportedly said Betson needed to do more than simply prove that the judge nodded off.

“If that happened, it would be necessary to show that, in consequence, part of the evidence did not find its way into the judge’s summing-up, or something of that sort,’ Rose reportedly said.

Arguments in the case won’t be heard for at least seven weeks.

Two other men convicted in the case are also awaiting a date for an appeal hearing.

The Court of Appeal has already dismissed an appeal by a fifth man, Kevin Meredith, 36, against his five-year sentence for conspiracy to steal.

JCK