A grand jury has been called to investigate the shooting of unarmed teenager Michael Brown by police officer Darren Wilson in Ferguson, Mo., but may take well into October to decide whether to charge the officer with a crime.

The grand jury—selected in the same way as normal trial juries—meets just once a week, which is part of the reason why it may take so long. There also, unsurprisingly, is a substantial amount of evidence to be reviewed, further extending the proceedings. Lead prosecutor David McCullough offered mid-October as the “target date” for his team to finish presenting evidence, at which time the grand jury would decide if there was sufficient proof to charge Wilson with a crime.

This announcement came as Attorney General Eric Holder arrived in Ferguson to meet with local leaders. “Our investigation into this matter will be full, it will be fair, and it will be independent,” Holder wrote in the St. Louis Post-Dispatch, and he also hopes that his efforts will help in “bridging persistent gaps between law enforcement officials and the communities we serve.”

Holder’s visit comes at a time where tensions appear to be cooling, at least a little. While there were 47 arrests across Ferguson last night, both protestors and police refrained from using the dangerous Molotov cocktails and tear gas that marked much of the last 10 days.

Depending on what happens with the grand jury investigation, though, this return to a relative level of peace may be short-lived.

[via ABC]