BRASILIA (AFP) - Brazilian police on Tuesday (March 19) arrested a teenager suspected of involvement in planning last week's high school shooting that left eight people dead and shocked a country long-used to deadly gun violence.

The 17-year-old was initially detained on Friday, but later released after denying taking part in the attack near Sao Paulo by two ex-pupils, who committed suicide.

A judge ordered the boy's arrest after police obtained new evidence from his home and cell phone, and those of the killers, a police official in Sao Paulo told AFP on the condition of anonymity.

The teenager, a former classmate of one of the attackers, can be held for a maximum 45 days without charge.

Brazil is one of the deadliest countries in the world, with 64,000 murders in 2017 - a rate of almost 31 per 100,000 inhabitants, or three times higher than the level the United Nations classifies as endemic violence.

The shooting has fueled debate over whether far-right President Jair Bolsonaro's measures to relax gun ownership rules, or images from similar such mass shootings on US school and university campuses, were to blame for the attack.