HOUSTON » A dog's sniff helped put Curvis Bickham in jail for eight months. Now that the case against him has been dropped, he wants the world to know that the investigative technique that justified his arrest smells to high heaven.

The police told Bickham they had tied him to a triple homicide through a dog-scent lineup, in which dogs choose a suspect's smell out of a group. The dogs are exposed to the scent from items found at the scene of a crime, and are then walked by a series of containers with samples swabbed from a suspect and from others not involved in the crime. If the dog finds a can with a matching scent, it signals—stiffening, barking or giving some other alert its handler recognizes.

Dogs' noses have long proved useful to track people, and the police rely on them to detect drugs and explosives, and to find the bodies of victims of crime and disaster. A 2004 report by the FBI states that use of scent dogs, properly conducted, “;has become a proven tool that can establish a connection to the crime.”;

Scent lineups, however, are different. Critics say that the possibilities of cross-contamination of scent are great, and that the procedures are rarely well controlled. Nonetheless, although some courts have rejected evidence from them, the technique has been used in many states, including Alaska, Florida, New York and Texas, said Lawrence J. Myers, an associate professor of animal behavior at the Auburn University College of Veterinary Medicine.

In particular, the methods of the dog handler in Bickham's case, and in a half-dozen others that are the basis of lawsuits, have come under fierce attack.

The handler, Deputy Keith A. Pikett of the Fort Bend County (Texas) Sheriff's Department, is “;a charlatan,”; said Rex Easley, a lawyer in Victoria, Texas, who represents a man falsely accused by the police of having murdered a neighbor. Pikett, the lawyer said, “;devised an unreliable dog trick to justify local police agencies' suspicions”; for producing search warrants and arrests.

Pikett, who declined to be interviewed, works in the town of Richmond, southwest of Houston, but he has served as a busy consultant to law enforcement agencies around the state, using his home-trained bloodhounds - he has given them names that include Columbo, Quincy and Clue - to sniff out crime. A native of Buffalo, N.Y., he has by his own estimate in court testimony performed thousands of scent lineups since the 1990s. His lawyer said the techniques were effective.

Thomas Lintner, the chief of the FBI laboratory's evidence response team unit, said the agency used scents only to follow a trail to a suspect or to a place associated with him, and not to identify one person out of several. The 2004 FBI report warned that dog scent work “;should not be used as primary evidence,”; but only to corroborate other evidence.

In several of the cases that were based on Pikett's dogs, however, the scent lineups appear to have provided the primary evidence, even when contradictory evidence was readily available. Bickham spent eight months in jail after being identified in a scent lineup by Pikett's dogs, until another man confessed to the killings. In an interview, Bickham scoffed at the accusation that he had taken part in three murders, noting that he has been hobbled by bone spurs and diabetes and is partially blind.

Ronald Curtis, another Houston man jailed on the basis of Pikett's dogs, was released from jail nine months after being accused of a string of burglaries. Store videos showed that the burglar did not resemble him. “;Nobody was listening,”; Curtis said.

Both he and Bickham are filing civil lawsuits over their treatment in federal court on Wednesday.

The first person to file such a suit, in January, was Michael Buchanek, a retired captain with the Victoria County, Texas, Sheriff's Department and a client of Easley. After Pikett's dogs identified him, Buchanek said the police “;just kept telling me, 'the dogs don't lie—we know you did it.' “; After months of uncertainty, DNA evidence implicated another man who later confessed to the crime.

As Easley began to dig in on the case, he sought the opinion of animal investigation experts who reviewed Pikett's work and responded with incredulity. Robert Coote, the head of a British canine police unit, reviewed videos of Pikett's scent lineup in the Buchanek case and stated, “;If it was not for the fact that this is a serious matter, I could have been watching a comedy.”;

Easley shared his findings with colleagues at the Innocence Project of Texas, a legal defense organization, which released a report last month that excoriated dog scent lineups as a “;junk science injustice.”; Jeff Blackburn, the chief counsel for the group, said Pickett merely gave the police the match they had hoped for.

Myers, the animal behavior expert, suggested that handlers like Pikett might believe in the dogs and the methods, but might allow samples to become contaminated or inadvertently allow the dogs to pick up on subtle, even unconscious signals from handlers or detectives. “;They just don't realize they're doing it wrong,”; he said.

Randall Morse, an assistant Fort Bend county attorney who is representing Pikett, said the dogs provided information, not conclusions of guilt or innocence.

“;Pikett doesn't arrest anybody,”; Morse said. “;Our dogs don't say ,You murdered somebody. They don't even say, You committed a crime. They just say, We picked up your scent.”;

Morse said scent lineups had proved their worth, as in the case of Bart Whitaker, a Texan who hired friends to kill his family in 2003. Pikett's dogs helped identify the trigger man from eight suspects. Whitaker is now on death row, and his accomplices are in prison.

“;We believe in this stuff,”; Morse said.

Blackburn of the Innocence Project noted that the Whitaker case involved a great deal of corroborating evidence beyond the dogs.

“;Our estimate right now is we've got 15 to 20 people who are in prison right now based on virtually nothing but Pikett's testimony,”; he said. “;That's a big problem.”;

Donna Hawkins, a spokeswoman for the Harris County district attorney's office in Houston, said she could not comment on the dispute over dog scent lineups or on the re-examination of cases that involved them. “;Cases will be evaluated on an individual basis, considering all relevant evidence,”; Hawkins said.

Bickham said he had lost his home while in jail and had struggled to restart his barbecue stand; he sold his cars to hire his lawyer. These days, he said, he is easily agitated, cries readily and is taking antidepressants.

“;I lost everything,”; Bickham said, because of “;a nothing case.”;