US police are searching for an escaped inmate and a prison officer who may have helped the convicted murderer break out, with investigations turning to whether the pair had a romantic relationship.

Efforts to find inmate Casey White and corrections officer Vicki White increased on Tuesday, as investigators announced a warrant had been issued for Ms White’s arrest.

The pair, who were last seen leaving an Alabama jail on Friday (US time), have multiple law enforcement agencies looking for them, including the FBI and US Marshals, the Lauderdale County Sheriff’s Office confirmed.

Prior to the warrant, it was unclear whether Ms White was a willing participant in the escape, investigators said.

According to the statement, prisoner White left the Lauderdale County Detention Centre on Friday morning in the custody of Ms White, the prison’s assistant director of corrections. The pair are unrelated.

Authorities say Ms White had told fellow corrections officers she was taking the inmate to court for a mental health evaluation – no appointment had been scheduled.

Lauderdale County Sheriff Rick Singleton said on Tuesday the police vehicle Ms White drove was found abandoned in the car park of a local shopping centre.

He said police were sifting through surveillance footage of the pair’s last known location, and that the vehicle went straight from the prison to the parking lot.

Sheriff Singleton confirmed Lauderdale County Detention officers did not know the two were missing until late on Friday afternoon, when calls to Ms White’s mobile went straight to voicemail.

He said “indications are” that Ms White, a 25-year veteran with the sheriff’s office, assisted in the escape of the inmate.

According to Sheriff Singleton, Ms White had filed paperwork for her retirement on Thursday. Friday was her last day of work.

Mr Singleton called Ms White an “exemplary employee” and noted that she had sold her house a month ago.