Wyatt Earp couldn't. Texas Rangers couldn't. But Enrique Mercado can and does. He chases murderers and rapists and child molesters across international lines to wherever they're hiding out.

In the past 12 years he's pursued 290 alleged criminals, murderers mostly, down into Mexico. And so far he has succeeded in persuading Mexican law enforcers to prosecute 70 of them. Think of him as an international bounty hunter with a license to incarcerate. Or, more correctly, a license to ask foreign governments to prosecute.

Mercado is the special-agent supervisor of what's known as the Foreign Prosecutions Unit of the California Department of Justice, a small office that has grown to the point where it now helps prosecutors nationwide file warrants for felons hiding south of the border. He runs his unit out of third-floor offices at the corner of Beech and India, a small corner section of the state's Bureau of Investigation.

"Most of the cases I work on are suspected murderers who flee to Mexico," he says. "Cases like -- remember the Hatfields and the McCoys? This guy, this kid, Pablo Osegura, killed a member of his own family. It was a San Mateo County Sheriff's office case, back in 1992.

"This murder was the latest in a long line. Family thing. More than 30 murders, going back years. It started back in Michoacán. One faction would murder a family member [in San Mateo], and then another family member would go back to Michoacán and murder one of their family.

"And the way I understand it, this kid was told to 'Do the right thing' for the family. I don't think he knew why. The feud had been going on so long, they forgot why they were doing it. It could be the nephew used a profane word to the uncle. Not showing respect for elders. Or over women. Most murders start that way. Staring at another guy's girlfriend. Pride, drink."

San Mateo sheriffs lost sight of Osegura, but when Mexican federal police arrested him on narcotics charges in Reynosa, Tamaulipas, a Mexican town that borders Texas, they contacted Mercado, whom they knew. "I went out. We took the case over there and filed it with the Mexican federal authorities. They prosecuted him for homicide and gave him 22 years, on top of 7 years for the narcotics charge. So 29 years total prison. Sad. I don't think he was older than 21."

That was one of Mercado's more successful cases, the result of a 40-year liaison with authorities throughout Mexico, a rapport developed by Mercado and his first boss, Ruben Landa -- who, Mercado says, single-handedly created the office for the California State Bureau of Investigation. The office has such luster that now the Department of Justice in Washington, D.C., recommends Mercado's office when police in any U.S. state need help nailing a fugitive who's fled to Mexico or beyond.

When he's not traveling, chasing down felons from Mexico City to Monterrey, Mercado's here on Beech, knocking cases into shape. "We have [acted] for Michigan, Pennsylvania, Nevada," he says. "I've just done some cases for Oregon, Washington, Utah, and today we have this kid here from Colorado. He's a detective, he came all the way here with a homicide case. We helped him put it together. We're going to take it to Mexico. The guy he wants is in Querétaro, north of Mexico City."

The "kid" wanders in. Detective Michael Schaller, from El Paso County sheriff's office in Colorado Springs, Colorado.

"We brought the case out here and filed it yesterday with Enrique," says Schaller. "The suspect murdered a roommate in a financial deal. For money. He fled about eight months ago. He's a Mexican citizen. We were able to use close friends, so we have good leads as to where he is."

Why can't Schaller's department just ask Mexican authorities to send the suspect back to Colorado? This is the crux of the whole issue and the reason Mercado's office exists. Mexico will not allow its citizens to be extradited, even if they have committed serious crimes.

"Crimes committed in a foreign country by a Mexican citizen against a Mexican citizen or against a foreign citizen," states article IV of its penal code of procedures, "or by a foreign citizen against a Mexican citizen will be punished in Mexico, if...the accused be in the Republic of Mexico...has not been definitely tried in the country where he committed the crime, and the crime with which he is charged be a crime both in the country where it was committed and in the Republic of Mexico."

This means police authorities in the U.S. have to find where the Mexican fugitive is hiding, create evidence for a case that will stick before a Mexican court, and physically take it down to federal prosecutors in the town where they believe the fugitive is hiding.

Sometimes it's easy, as with the case of Martin Meza. "We had this suspect, a young kid who killed one person and wounded another," says Mercado. "He fled to Mexicali. They detained him there and notified us. When I went over there and talked to him, he said he was a Mexican citizen. I found out he was born in Mexico, but as a little child he was brought to Los Angeles. He was raised there. He was a U.S. citizen. And he didn't speak any Spanish. I asked him, 'You sure you're not a U.S. citizen?' He said, 'No. No.' I say, 'Okay. If you're a Mexican citizen, we'll file a case here, and you'll be prosecuted here.'

"I don't think he believed me. So we came back and we got the documents -- all the paper reports -- legalized and translated, and then we presented it to a federal prosecutor in Mexicali. And he went to trial. Over there they don't have jury trials. There's not courtrooms. They call their process 'paper trial,' because everything's done by correspondence between the prosecutor and the defense attorney. They have to submit arguments in written form."

Mercado says that changed the murderer's mind. "Somehow he escaped from jail. He returned back to the L.A. area. He turned himself in. He said he didn't like the prison over there. He said he really was a U.S. citizen. So they prosecuted him over here in West Covina and sentenced him to 44 years to life in state prison."

But usually it's a long formal process. "First, after arriving at the airport and checking into a hotel, we'll meet with the chief federal prosecutor in that state," says Mercado, "and he will assign a federal attorney to take up the [issue] with us. In each case we will take down an English file and a Spanish file. We'll have four copies of each required by their legal system. We will sit there, and the attorney will go over it, review the case, review any questions. They're required by law to deal with it. Mexican federal penal code, article 4, gives authorization [for us to] file these cases."

The problem is, U.S. prosecutors must file their warrants through Mexico's federal police, even though it is the state judicial police whose job it is to chase felons. To get around this, Mercado often pays a discreet visit to the state police to let them know who he's looking for, after handing over his files to the federal authorities.

But the biggest problem is the neighbors' differing legal systems themselves. While the U.S. system is based on English common law, the Mexican law derives from Napoleonic and Roman law.

According to Juan Jose Briones, the result is that criminal procedures are completely different in California than in Mexico. Briones, a close colleague of Mercado's, is international case coordinator for the San Diego County DA's office. "In Mexico, the prosecutors are also the investigators, with the assistance of the [state] judicial police. Whereas in the U.S., the prosecutors have nothing to do with the investigation itself. The police departments do the investigation, and the prosecutors do the prosecution.

"In Mexico the prosecutors do both. They investigate and they prosecute. Because of historic reasons, they are doing away with the police investigation and getting the prosecutors involved more in the investigation."

This apparent lack of trust among Mexican authorities for their police is now affecting the evidence that Mercado and Briones take to Mexico. "Until recently the elements in a Mexican investigation were basically the same as in a U.S. investigation: we would give them police reports, witness statements, autopsy reports, death certificate, and we got convictions.

"But recently some Mexican judges are releasing persons who are already in custody, because they say the [American police] reports constitute [only] hearsay. They say, 'We need you to go and interview the witnesses again, have [witnesses] give a statement directly, instead of through a [police] officer, and have them sign at the end of their statement, as we do in Mexico.' "

"I think the reason behind it is that they do not have a [live, jury] trial in which the witnesses will have an opportunity to say the same thing again. So they want to get it 'straight from the horse's mouth' the first time, and with his signature because that way you can say, 'You read this and you signed it.'"

But Briones says he and Mercado do not accept Mexico's dismissal of U.S. police reports. "We feel that the [Mexican] judges are wrong, and we can prove that they're wrong. In international law, you cannot request a country to apply your laws [to its investigation]. How would we like it if Japan gave us the Japanese code and said, 'Do your investigations this way'?"

"Listen, sir. You do whatever you want, but I'm advising you: don't file the case the way it is. Don't do it."

Enrique Mercado is talking to his other big problem. A renegade police department somewhere in California that wants to go chase their felon in Mexico independently.

"I won't give you that particular police department's name," Mercado says to me. "I think they've learned their lesson, but apparently they sent two detectives who went and met with some Mexicans in Mexico City. They sent me the case to review it and have it translated. But when I looked at it I said, 'No, this is not acceptable. The case you bring to us to file in Mexico has to be prosecutable here. We're not going to file cases [over there] just so you can close them [here].' They do that! But this PD filed it anyway. And, naturally, the Mexicans kicked it back to them. They still have it."

What does get results in Mexico, say Briones and Mercado, is attitude. "We always try not to be pushy, not to be seen as coming down to tell Mexican authorities what to do. Because they do resent that," says Briones.

"We go all over," says Mercado. "Oaxaca. Jalisco. Veracruz. But we don't say, 'Here's the case, we want you to do this...' No. 'We request your assistance....' It's the way you present yourself. We go with respect, because it is their laws, their country."