To protect Calgary police investigative techniques, their controversial cellphone surveillance device will remain so secretive, not even the make and model can be released to the public, according to a court ruling released Monday.

The judge's decision was given to lawyers in August but it took two-and-a-half months for them to agree on redactions, which appear throughout the 17-page decision.

The MDI (Mobile Device Identifier) technology — which mimics cell towers and intercepts data from nearby phones — is controversial in part because in at least one Canadian case, prosecutors have taken watered down plea deals rather than disclose information related to the device.

Barakat Amer and Tarek El-Rafie were arrested along with five others in 2016 as part of a major police gang investigation called Operation Hybrid. During the investigation, Amer and El-Rafie were the targets of several MDI deployments.

Earlier this year, lawyers for the pair — who are headed to trial on 17 counts of attempted murder — argued they had a right to some evidence related to the device and the deployments.

In this case, investigators said they gained no relevant evidence against the pair so they destroyed all of the data.

Court of Queen's Bench Justice Glen Poelman initially agreed with defence lawyers Kelsey Sitar and Clayton Rice and granted them the right to question the CPS officer involved in using the MDI regarding its make, model, features and the circumstances that may or may not affect its use.

But after Poelman's first ruling, prosecutor Brian Holtby invoked a section of the Canada Evidence Act that allowed the Crown to argue — at an in-camera hearing — that disclosing CPS investigative techniques would be contrary to public interest.

Now, Poelman has ruled the police investigative techniques are privileged, and he prohibited the release of the make, model and software of the MDI as well as "any further information which would have the effect of disclosing the technique by which MDI obtains cellphone identifier information."

Poelman noted in his unsealed decision that according to evidence from Sgt. Scott Campbell, CPS has used its MDI in 14 investigations and continues to use it.

But the fight isn't over for defence lawyers, who will make further submissions that their clients' rights to a fair trial outweigh the police privilege. If Poelman agrees, and if the police and prosecution refuses to hand over the information, defence lawyers would seek to have the charges against their clients dropped.

In recent years, RCMP have been so secretive about their use of the devices during investigations that in certain cases prosecutors have offered extreme plea deals and might have stayed charges rather than disclose information related to the technology.

Last year, six Montreal gangsters originally charged with first-degree murder pleaded guilty to conspiracy to commit murder, and another to accessory after the fact, after the Crown declined to disclose details of the technology to defence lawyers.

In March, Quebec prosecutors stayed 36 charges against suspected members of the Montreal Mafia. The Crown said that decision was based on "many factors," but the move did raise speculation prosecutors were concerned about evidence gathered using MDI devices that would have to be handed over to defence lawyers.

No other Canadian police agency, including the RCMP, Ontario Provincial Police or Winnipeg police, has disclosed the make and model of their devices.