Dorian Johnson, a key witness in the shooting death of Michael Brown in Ferguson, Missouri, was arrested late Wednesday for interfering with an arrest. Johnson was walking with Brown on the day the latter was fatally shot by a white police officer on Aug. 9, 2014.

According to St. Louis police, Johnson was with a group of people who were possibly armed with guns. He was accused of preventing a police officer from making an arrest, and was also seen throwing suspected narcotics on the ground, BBC reported, citing Leah K. Freeman, a spokeswoman for St. Louis County Police.

Charges against Johnson are expected to be filed on Thursday, reported. The arrest came hours after reports emerged that Johnson is suing the city of Ferguson, its former police chief Thomas Jackson and Darren Wilson -- the officer who fatally shot Brown. Johnson claimed in the lawsuit that he was wrongfully stopped and fired on on the day Brown was shot dead, NBC News reported.

“Officer Wilson acted with either deliberate indifference and/or reckless disregard toward” according to Johnson's lawsuit, which seeks $25,000 in damages. The lawsuit also claims that the city of Ferguson and Jackson “facilitated, encouraged and/or instigated” biased police behavior, including the use of “excessive force” against Brown and Johnson.

While Brown was fatally shot by Wilson in the confrontation last August, Johnson escaped unhurt, and became a key witness in the case. In November, a grand jury decided not to indict Wilson after a federal investigation found no evidence that Wilson had acted illegally.