Three Mexican brothers facing the gallows in Malaysia on drug trafficking charges managed to get their trial halted today amid claims that the evidence was tampered with.

The Gonzalez Villarreals - Luis Alfonso, 43, Simon, 36 and Jose Regino, 33 - were charged in 2008 with a Malaysian and a Singaporean after being arrested at an alleged drug-making factory.

The brothers were due to testify in court today but their lawyer Kitson Foong asked judge Mohamed Zawawi Salleh to halt the trial pending a review of the case by the Federal Court.

Foong had previously told the court the brothers should be freed because evidence had been tampered with but judge Zawawi dismissed the argument and ordered the trial to proceed.

"It is important... We believe that the court did not fully appreciate some of the testimonies with regards to the identity of the exhibits," Foong said.

"The exhibits from the time (the accused) were arrested to the time they were analysed are different," he added.

No date has been fixed for the Federal Court hearing.

The suspects were arrested at a factory in southern Malaysia in 2008 with police seizing 29.46 kilograms of methamphetamine and chemicals used to produce it.

Drug trafficking carries the mandatory death penalty by hanging upon conviction and trials usually take a long period to complete.

As of this February, there were nearly 700 prisoners, mostly men, on death row - more than two-thirds for drug offenses.

- AFP