Wichita ? The sister of a man accused of killing a teenage clerk at a convenience store says he had recently stopped taking medication prescribed for his mental illness.

Anthony R. Barnes, 40, is being held on $500,000 bond, charged with first-degree murder and aggravated assault. He is accused in the fatal shooting Monday night of Brian Hall, a 17-year-old high school senior.

Police said Barnes walked into a QuikTrip store and pointed a gun at a customer he thought had been laughing at him, then abruptly fired a shot into the head of the young clerk, who was behind the counter helping another customer.

Barnes then went outside and was smoking when officers arrived, police said.

Jeresia Williams, a sister of Barnes, said he was a schizophrenic known to “rant and rave sometimes all night long.”

“We’d all tell him to go take his medication,” she said. “He’d say he didn’t need it.”

Williams said her brother, who is about 6-foot-2 and 250 pounds, would sometimes threaten people on the street. She said relatives had called a crisis line a couple weeks ago to try to get help for him. She said they were told little could be done but to call 911 if he made other threats. Williams said Barnes then went to sleep and his rantings seemed to subside.

According to police reports, Barnes and been arrested in 2004 and accused of hitting a man repeatedly with a baseball bat. A disorderly conduct charge was dismissed because a witnesses did not appear.