A 16-year-old boy is the last of four teenagers charged with robbing and beating an 86-year-old man before killing him by tying a plastic bag around his head, authorities said.

The South Carolina Law Enforcement Division said the teen arrested Monday will be tried as an adult for murder.

The teen was 15 years old when he and three other people broke into Willie Johnson's Allendale home in June 2014, officials said. Three other teens — two 16-year-olds and one 15-year-old — were arrested a few weeks after the killing.

A SLED agent said in a sworn statement that the latest teen arrested confessed and implicated the other boys. It wasn't known whether the teen arrested this week had a lawyer.

Investigators said Johnson's body was found after he didn't answer his door for volunteer meal deliveries for several days.