Law enforcement officials this week challenged the honesty of a crusading undercover officer who arrested 10 percent of a small towns black population on drug charges. Former policeman Thomas Coleman conducted a one-man sting operation that led to the arrest of 40 black people, with 22 later sentenced to lengthy jail terms, including terms of 60, 99, and 434 years. The only evidence in the case was Colemans testimony that he sold them drugs. Four defendants have challenged their convictions, and in hearings law enforcement officials from Tulia and neighboring towns testified that Colemans police work was worthless. One described Coleman as a paranoid gun nut, and another called him a racist. Coleman conceded some of his testimony in the cases might be in error, but said he was a regular, normal human being, Texan.