FORT DRUM — A New Jersey judge will determine whether the former Watertown teen involved in the murder of a Fort Drum soldier is competent to stand trial.

Former Army Spc. Jamaal Mellish and his former girlfriend’s brother, Hannan Aiken, 18, formerly of Watertown, are accused of kidnapping and killing Cpl. Hayden Harris in December 2020 after a dispute the two soldiers had over swapping their vehicles.

The trial was expected to begin in October but has been put on hold until it can be determined whether Aiken is competent to stand trial, said Sahil Kabse, an assistant prosecutor in Sussex County, New Jersey, prosecuting the case.

“The competency issue must be determined before a trial date can be set,” he said.

A hearing will be held on March 3 in which Aiken’s attorney, public defender Thomas Militano, will argue that he wants to present his own expert to testify that the teen is not able to go on trial.

A state expert has determined that the teen can stand trial.

Testimony from the public defender and Mr. Kabse will be heard before Sussex County Judge Michael C. Gaus during the March 3 hearing.

Aiken, who was 16 at the time of the murder, is being tried as an adult. The two defendants are now expected to go to trial this spring, Mr. Kabse said. They will be tried together.

Mellish was preparing to represent himself, but has changed his mind. He filed a motion in December for his standby attorney, Joel M. Harris, to take over the case. Mr. Harris, who could not be reached for comment, would have been available to offer legal advice to Mellish and answer questions.

But Mr. Harris would now be his defense attorney.

Judge Gaus needs to grant Mellish the change. The judge could decide both issues from the bench at the March 3 hearing or issue a written decision.

A partial conference must still be held before a trial date is scheduled.

“I anticipate a return date will be shortly,” Mr. Kabse said. “Any other issues will be presented at the pretrial conference.”

The two defendants are accused of forcing Harris at gunpoint to ride in the backseat of a pickup truck for more than four hours to Byram Township, and then shooting him in the head. His body was found partially covered by snow next to a cul-de-sac in the northern New Jersey township.

Mellish allegedly agreed to swap his Chevrolet Silverado for Harris’s Ford Mustang in July 2020, months before the corporal was killed in December.

But Harris was dissatisfied with the circumstances of the transaction and wanted his Mustang back, which angered Mellish, prosecutors have said.

Harris was having trouble getting the pickup truck registered with the Department of Motor Vehicles.

The two soldiers allegedly agreed to return the vehicles back to each other. They met in a Glen Park parking lot, where Mellish ordered Harris in the backseat of the Silverado.

At that point, however, Mellish no longer owned the Mustang. He had sold the sports car several months before the killing.

Fort Drum reported Harris missing on Dec. 17 and his body was discovered the next day. Aiken and Mellish were apprehended by the Jefferson County Sheriff’s Office after a deputy stopped them in the Silverado on Arsenal Street in Watertown.

The teen allegedly held Harris at gunpoint in the backseat during the more than 300-mile drive to New Jersey, while Mellish drove the corporal’s pickup there.

Prosecutors have video evidence from a cellphone showing Aiken brandishing a handgun just hours before meeting up with Mellish.

The teen allegedly gave a statement to police pointing out that Mellish was the killer.

Mellish remains behind bars in a New Jersey correctional facility.

Aiken is being held at the same facility after he was moved there following some incidents in which he was involved at a juvenile facility.

The Army posthumously promoted Pvt. Harris to the rank of corporal.