Police in Arkansas wish to unlock an iPhone and iPod belonging to two teenagers accused of killing a couple, according to the Associated Press (AP).
Less than a day after its San Bernardino announcement, the FBI agreed to help in the homicide case.
Syed Farook and his wife were shot dead after killing 14 people in December.
A judge agreed to postpone the Arkansas case on 28 March to allow prosecutors to ask the FBI for help.
Hunter Drexler, 18, and Justin Staton, 15, are accused of killing Robert and Patricia Cogdell at their home in Conway, Arkansas last July.
Staton had been raised as a grandson by the Cogdells.
"We always appreciate [the FBI's] cooperation and willingness to help their local law enforcement partners," Faulkner County prosecuting attorney Cody Hilland told the AP.
An attorney for Mr Drexler told the AP he was "not concerned" about any data on the phone.
Previously, the FBI had asked Apple to write new software that would allow it to gain access to Farook's iPhone.
However, the company refused, arguing it would be wrong to compromise the security of one of its devices since that might lead to vulnerabilities in many other iPhones.

The 34-year-old rejoined the New Lawn side in July 2016 and was ever-present as they won promotion to League Two last season.
He made 144 appearances in his first spell with the club before spending the 2015-16 season with Gateshead.
Mark Cooper has signed defenders Lee Collins and Callum Evans and midfielder Reece Brown as they prepare for their first season in the Football League.

David Harris, 68, who had become "besotted" with another woman, was found guilty of offering to pay an undercover policeman £150,000 to murder Hazel Allinson.
His Old Bailey trial heard he wanted to inherit her West Sussex home and elope with sex worker Ugne Cekaviciute, 28.
The Court of Appeal confirmed papers had been lodged for an appeal.
Harris, the former producer of the police drama series The Bill, had claimed he was researching a spy novel and denied solicitation to murder at his trial.
But the retired producer was caught when the police officer posing as a would-be hitman taped a conversation in which Harris said he was "100% sure" he wanted his partner dead.
The jury was told Harris had mounting debts and was desperate to inherit his partner's £800,000 home in Amberley and set up home with Ms Cekaviciute.
The Old Bailey was told Harris had approached London mechanic Christopher May in March 2016 and said: "I'm offering you £250,000 to kill my wife."
In November 2016 he met an undercover policeman posing as a hitman called Chris in the car park of Sainsbury's in Balham, south London.
They were introduced by a 6ft 3in "man mountain" called Zed, to whom Harris had previously given Ms Allinson's details and a photograph.
Unknown to Harris, Zed, whose real name is Duke Dean, had already reported him to City of London Police, the court was told.
Jailing Harris for 17 years in July, Judge Anne Molyneux QC said: "For your pipe dream, for your obsessive infatuation with a young woman, Ms Allinson, who had protected and nurtured you, was to die a painful and terrifying death in an isolated spot.
"Her death was to fund your life. You had used her until she had outlasted her usefulness to you."

Walters, 33, has signed a two-year deal after spending seven years with the Potters, scoring 62 goals in 269 appearances.
He becomes Burnley's second summer signing after full-back Charlie Taylor joined from Championship side Leeds.
Walters' move means the Clarets now have five Republic of Ireland internationals in their squad.
He joins defenders Stephen Ward and Kevin Long, and midfielders Jeff Hendrick and Robbie Brady at Turf Moor.
Clarets striker Andre Gray, who has reportedly rejected a new contract, has been linked with a £15m move to fellow Premier League side West Ham.
Find all the latest football transfers on our dedicated page.
The FBI has offered to unlock another iPhone for police after revealing it could access the handset used by San Bernardino killer Syed Farook.
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Forest Green Rovers goalkeeper Sam Russell has signed a new one-year deal.
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A retired TV producer is to appeal against his conviction for trying to hire a hitman to kill his partner.
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Burnley have signed Republic of Ireland striker Jon Walters from Stoke City for a fee that could reach £3m.