A caravan of demonstrators honoring Martin Luther King, Jr. on Monday, while attempting to shine a light on police misconduct, were met in Alameda by a man brandishing a rifle.

The roving demonstration arrived in Alameda at the home of Alameda County District Attorney Nancy O’Malley, where the individual confronted the group.

The firearm was not discharged, but the demonstration at O’Malley’s home to seek the prosecution of a BART cop involved in Oscar Grant’s death was cut short.

The Alameda Police Department announced on Tuesday afternoon that it is launching an investigation.

After Alameda Police receiving reports of the MLK caravan entering Alameda they received reports of “multiple individuals with firearms” the police department said in a statement on Tuesday.

The caravan was organized by the Anti Police-Terror Project, an Oakland-based group that has long sought reforms at the Oakland Police Department and other local law enforcement agencies.