HOUSTON --A man is in jail, accused of killing a Harris County deputy constable. The officer's body was found early Tuesday morning, and by the end of the day, a suspect was in custody. Homicide detectives are questioning that suspect in downtown headquarters and talking to a female witness. They've interviewed a number of people in an attempt to find out what who murdered the deputy. After trailing their suspect as he walked with friends along Laura Koppe, a Houston police tactical unit closed in and made an arrest. It happened around 6:30pm Tuesday, the man in the back of the patrol car didn't resist. Officers say they had a capital murder warrant for the suspect. The victim is Harris County Precinct 4 Deputy Constable Ronnie Brewer. "I just don't know who would want to hurt him. He really don't do harm to anybody. He really just try to help people," Tenille Brewer, his niece, said. Brewer's family was in disbelief when they heard the news. The deputy was found shot to death around 1:30 Tuesday morning inside his car in northeast Houston. His maroon sedan had crashed into a pole. He was wearing plain clothes and was off duty. His parents live less than a mile away, but the investigation focused on an apartment complex nearby. Police believe robbery was the motive, but aren't revealing the circumstances. His grieving colleagues say it doesn't matter. "We don't know what he was doing out there. It's really irrelevant. The guy was obviously a victim of a homicide," said Asst. Chief Mark Herman with the Harris County Pct. 4 Constable's Office. Brewer had been with Precinct 4 for 10 years, most recently assigned to toll road division. He was also a proud member of the honor guard and a desert storm veteran. Family and friends describe him as caring and good natured. "My uncle, he was a very good, caring person. I mean he did anything he could for anybody," Tenille said. Along with the murder suspect, officers also arrested his friend. We've learned homicide investigators talked to him earlier in the day and cuffed him for outstanding city warrants. A woman was taken in as well as a witness. They've worked fast on this case. Precinct 4 has been told they should have answers soon. "We're hurt. This is something that impacts us and we want to know why; we want to ask a million questions but we know it's our turn to sit back and let the wheels of justice turn," Herman said. Brewer was 47 and lived in Porter. He wasn't married and had no children, although family members say he was a very active uncle. HPD has not released the name of that suspect in custody. Visitation and funeral services are pending.