Two separate syndicates, linked to the Mongols and Bandido bikie clubs, allegedly used the method to pass methamphetamines, cannabis and pain killers into the Arthur Gorrie Correctional Centre and the Maryborough Correctional Centre for more than three months.

In total, 19 people have been charged with drug smuggling offences, including seven inmates.

Two of the men charged are convicted murderers, Taskforce Maxima Superintendent Mick Niland said.

During the operation police seized five ounces of the drug ice, more than 100 strips of the pain killer buprenorphine and two ounces of cannabis.

Five mobile phones and several sim cards were also seized from within the prisons.

Also seized was $21,000 cash from outside the prison believed to be linked ot the alleged drug trade.

Police also claim inmates were trying to purchase and on-sell weapons on the outside to earn cash for themselves.

Detective Inspector Terry Lawrence said there was no suggestion Queensland Corrective Services staff or lawyers were involved.

However investigators admit they don't know how long criminals had been using fake legal letters to sneak drugs into prisons.

"To a layperson, it would look easy. We really don't want to describe the methodologies," Superintendent Niland said.

He defended Queensland Corrective Services, saying they did an "excellent job" and worked with police to shut down the syndicates.

"They've worked in partnership with us from day one and even today, in the closure of the operation, junior officers from within corrective services and senior management were all very happy with the outcomes of this investigation," he said.