Editor's note: This story has been revised to correctly note when and where the two defendants who are in custody were arrested.

Authorities have arrested two juveniles and are searching for a third in connection with last week's triple murder in southeast Marion. All three are charged with first-degree murder.

One defendant is 12 years old. He was taken into custody Thursday at his home.

Another defendant, age 17, was arrested last week by Ocala Police Department officers after the killings had taken place. He was arrested in connection with a different case: a disturbance at his school. He was already in custody when the murder charges were brought.

The third defendant, age 16, remained at large Friday morning.

Earlier coverage: Third teen dies in SE Marion. 15 detectives on the case. Is a 'wannabe gang' responsible?

Earlier coverage: A deepening mystery | Another body has been found in SE Marion

The three victims - two 16-year-old girls and a 17-year-old boy - were shot at the same time on March 30, Sheriff Billy Woods announced during an emotional news conference at the county Emergency Operations Center in Ocala. The bodies were found in separate Ocklawaha locations on March 30, 31 and April 1.

Woods said the two defendants in custody made incriminating statements about their involvement in the shootings.

Sheriff's officials believe the three defendants and the three victims were engaged in vehicle burglaries, a practice known as "car hopping." In such cases, thieves work an area looking for unlocked vehicles.

Woods would not say how many firearms were involved in this case. But he did say that one gun was obtained by the defendants in a vehicle burglary.

Woods said robbery was the motive for the three killings, though he did not elaborate. All six were together at the time of the deaths.

"They took a life without thought. They deserve the full extent of the law," Woods said during the news conference. At one point, he choked up when thanking his staff and the other law enforcement agencies who are working this case.

He specifically thanked the Ocala Police Department, the FBI, the Florida Department of Law Enforcement, the U.S. Marshals Office, the State Attorney's Office, and also the public and the media.

Sheriff's officials said their agency has had minimal contact with the defendants in the past.

Woods spoke to the mothers of the two defendants who are in custody. He expressed sympathy for them.

While Woods expressed shock and sadness, he also urged the public to help find the third defendant.

This story will be updated throughout the day.

This article originally appeared on Ocala Star-Banner: Sheriff: Youths ages 12, 16 and 17 responsible for triple murder