Members of the National Guard stand guard outside the Ferguson Police Department in Missouri November 28.

ST. LOUIS — The Missouri National Guard is starting to scale back its presence in the St. Louis area as angry protests over the lack of an indictment in the police shooting of an unarmed Black teenager ease, Missouri Governor Jay Nixon said on Tuesday.

St. Louis County police said on Tuesday they are probing who was responsible for setting fires, looting and destroying property last week after the announcement that a grand jury decided not to indict White Ferguson police officer Darren Wilson for killing 18-year-old Michael Brown on Aug. 9.

One person of interest in the investigation is Brown’s stepfather Louis Head, St. Louis County police spokesman Brian Schellman said. Head was caught on video comforting Brown’s distraught mother after the Nov. 24 announcement of no indictment, and then turning to a crowd of protesters and screaming repeatedly: “Burn this bitch down.”

“Our department is currently looking into this as a part of the entire investigation that includes the arsons, looting, destruction of property, etc.,” Schellman said. The findings will be presented to the St. Louis County Prosecuting Attorney’s Office, he said.

Head could not immediately be reached for comment. Attorneys representing Brown’s family did not respond to a request for comment.

Protests have continued since Brown’s death, and were mostly peaceful in recent months until the grand jury announcement spurred a fresh outbreak of rioting. Protest leaders have said St. Louis County Prosecutor Bob McCulloch’s decision to announce the lack of indictment at night contributed to the unrest.

The protests eased by the Thanksgiving holiday, and Nixon said on Tuesday that the Guard had completed its duties within the city of St. Louis though it would continue to support law-enforcement agencies in Ferguson and other areas of St. Louis County. He said there were some 1,200 troops still stationed in the St. Louis area.

Nixon said in a statement he remained in touch with local and state law-enforcement officials to discuss the status of “the missions.” He said the officials had agreed there would be a systematic reduction in guard operations as conditions improved.

Guard troops were initially deployed to Ferguson for a short time in August during violent protests after Brown’s death. In both August and over the past week, they provided security at police and fire stations, utility substations, hospitals, shopping malls and sports stadiums.