I thought the territory of Brazil belongs to the Brazilian government? Do they have deeds for the land?
I feel bad for them. It's the human reaction to feel bad for them. But it's 2017. You can't go running around on land that you don't own throwing spears at people anymore. These people need to catch up with the times because their lifestyle isn't legal anymore.
If these people don't comply with the law and keep pretending it's the year 500 BC, obviously things like this are going to happen. It'd be better for everyone, them included, if they got birth certificates, government IDs, went to school, and started working + paying taxes.