Some criminals have switched to new iPhones as their "device of choice" to commit wrongdoing due to strong encryption Apple Inc has placed on their products, three law enforcement groups said in a court filing.

The groups told a judge overseeing Apple's battle with the U.S. Department of Justice on Thursday that, among other things, they were aware of "numerous instances" in which criminals who previously used so-called throwaway burner phones have now switched to iPhones. They did not list a specific instance of this practice.

The brief by the Federal Law Enforcement Officers Association and two other also cited a jailhouse phone call intercepted by New York authorities in 2015, in which the inmate called Apple's encrypted operating system "another gift from God."

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The government obtained a court order last month requiring Apple to write new software to disable passcode protection and allow access to an iPhone used by one of the shooters in the December killings in San Bernardino, California.

Apple asked that the order be vacated, arguing that such a move would set a dangerous precedent and threaten customer security.

Tech industry leaders including Google, Facebook and Microsoft and more than two dozen other companies filed legal briefs on Thursday supporting Apple. The Justice Department received support from law enforcement groups and six relatives of San Bernardino victims.

The law enforcement groups said in their brief that Apple's stance poses a grave threat to investigations across the country. 

They listed several instances where Apple previously turned over data, and in one case, that cooperation helped clear an innocent man suspected of a homicide.

Apple has said it respects the FBI and has cooperated by turning over data in its possession. "Apple complies with valid subpoenas and search warrants," Tim Cook said in a letter to customers last month.

The San Bernardino request is different, Apple says, because it requires them to crack a phone with a software tool that does not currently exist.

Law enforcement officials have said that Rizwan Farook and his wife, Tashfeen Malik, were inspired by Islamist militants when they shot and killed 14 people and wounded 22 others on Dec. 2 at a holiday party in San Bernardino. Farook and Malik were later killed in a shootout with police, and the FBI said it wants to read the data on Farook's work phone to investigate any links with militant groups.