For somewhere on the vast rail network is Rafael Resendez-Ramirez, a man whom the FBI suspects of at least eight murders, perhaps many more. He has been riding the rails for 20 years, drifting across America from Miami to St Louis.
There is much that is deeply mysterious about Resendez-Ramirez - if that is his real name. The FBI's Most Wanted poster lists 30 aliases, including Jose R Angel, Daniel Edward Arnold, Jose Konig Mangele, Aerrjel Martinez, Angel Joseph Martinez and Carlos Cluthier Rodriguez. A native of Peubla in Mexico, he has been repeatedly imprisoned and deported only to return, working as a day-labourer across the country before disappearing again on the freight cars that slowly criss-cross America.
The killings started at 3 o'clock one August morning two years ago. Two University of Kentucky students were walking back from a party, using the rail lines as a short cut, when they were attacked by a man described as Hispanic, of medium height and speaking reasonable English. Christopher Maier was killed; the woman was raped and stabbed in the neck.
Then Dr Claudia Benton was found dead in her bedroom in a Houston suburb a few blocks from the railway in December 1998. She had been stabbed, bludgeoned and sexually assaulted. Fingerprints were found which identified the suspect as Ramirez-Resendez, the first time his name had surfaced.
Murders then came thick and fast. Norman Sirnic and his wife Karen were beaten to death in their bedroom with a sledgehammer in April this year; three miles away, Josephine Konivicka was pickaxed to death on 4 June. Noemi Dominguez was beaten to death near Houston the next day. On 15 June, George Morber and his daughter, Carolyn Frederick were killed in their mobile home in Gorham, Illinois. Morber had been shot; Frederick had been beaten and sexually assaulted. Fingerprint evidence again connected Resendez-Ramirez.
He is a spree killer, the police say, killing for no obvious motive with little clear pattern beyond the railway. And so the Railway Killer he has become. "Wherever he decides to stop, he stops," said FBI spokesman Mike Fabregas. "He has no connection whatsoever with his victims. They are just in the wrong place at the wrong time." He uses any weapon which is handy. Sometimes sexual assault follows; sometimes not. Sometimes he steals, sometimes not.
Resendez-Ramirez, if it is him, is resourceful. He has documents to support his many assumed names. He has changed his appearance. He has spent 11 of the last 20 years in jails in California, Texas, Florida and New Mexico for offences relating to drugs, weapons and theft - never murder.
The immigration authorities first picked him up in Brownsville, Texas, in 1976, when he was just 16, apparently; but then there are seven birth dates in his records. He was deported to Mexico. Three years later, a man called Jose Angel Reyes was arrested in Miami for breaking and entering a house and beating up the resident to get his car keys. "He beat the tar out of the guy," a Miami police spokesman told the Miami Herald. He was sent to prison for 20 years, but served only five and was released in 1985 and deported. A year later, Jose Reyes-Resendez was picked up by the San Antonio immigration authorities and given 18 months for falsely representing himself as a US citizen. He was deported again in October 1987. A year later he was arrested in St Louis, sent to prison and deported in March 1991. In August 1992, Antonio Martinez was arrested for burglary in New Mexico and was deported. Next April Carlos Rodriguez was jailed in Amarillo Texas for evading arrest. Pedro Angel Jaramillo was arrested in August 1995 in California for trespassing and carrying a loaded gun. All were the same man, fingerprint evidence shows. US immigration officials arrested him again earlier this month, it turns out - but simply deported him as they did not realise he was wanted.
What is far from clear is how the petty criminal becomes the mass murderer, if it is the same person. "There's nothing in the file that would distinguish him from any other inmate," said Florida Corrections spokeswoman Debbie Buchanan. "It's almost as if he woke up some day and snapped," said Texas Police Sgt Ken Macha, who is investigating one of the killings. "There's no clear progression of violence." He has left written messages about America and the Middle East at the murder sites, but it is not clear how these relate to the killings. He is on the FBI's Ten Most Wanted list, up there with Osama bin Laden, the man America blames for the embassy bombings in Kenya and Tanzania, and the leader of the Tijuana drug cartel.
America is fascinated with serial killers: this summer there is the new Hannibal Lecter book, and a Spike Lee film on Son of Sam. There are many such cases - the I-70 murders, the Great Basin case, the Missouri river killings - but no suspect in most. Resendez-Ramirez seems to incarnate a fear of mayhem coming up from south of the border, bringing terror and death. His victims are white and respectable, not prostitutes like those found dead in Spokane or Kansas City.
The FBI's "Operation Stop Train" has led to thousands of officers spreading out to search freight cars across America. Dozens of Hispanic drifters have been questioned; some have been chased and harassed merely because they look similar. But Jose, Carlos, Rafael or whatever his name is remains at large, somewhere between Mexico and the Arctic Circle.