KOBE (Kyodo) Two teenage boys were arrested Thursday on suspicion of participating in the murder of a 60-year-old disabled homeless man in Himeji, Hyogo Prefecture, last October, police said.

Makoto Amazutsumi, whose was physically impaired, was burned to death under a bridge along the Yumesaki River where he lived. The fire is believed to have been started by a firebomb.

The two suspects are a 15-year-old junior high school student and an 18-year-old high schooler, police said.

They also served arrest warrants on two other boys, both 16, who are already under arrest for alleged extortion and are also suspected of involvement in Amazutsumi’s slaying, investigators said.

The four boys are friends and had repeatedly abused homeless people, including Amazutsumi, since last summer.

Shortly before Amazutsumi’s death, they verbally abused homeless people and threw stones at them.

Police believe the harassment escalated, culminating in the firebombing.

The 16-year-olds told police they threw a firebomb toward the area where Amazutsumi lived because they were frustrated, the investigators said.

The boys allegedly knew the victim’s disabilities may prevent him from escaping.

Amazutsumi lived beneath the bridge for several years.