The woman witnesses say drove her van into a school bus, killing four children in Cottonwood, Minn., last week, apparently had two earlier traffic encounters with law enforcement. Both times officers issued tickets and gave her a ride home without checking her immigration status.

Olga M. Franco's ability to remain in Minnesota, using a phony name and ID card, has prompted outrage from the U.S. Congress to blogs.

But police chiefs in southwestern Minnesota offer a practical and ethical explanation: They say they don't detain minor offenders because immigration officials haven't come to pick up them up in the past. And they don't want to engage in racial profiling.

"Should a police officer hold everyone who is stopped without a license to substantiate that they are or are not who they say they are?" asked Rob Yant, public safety director in Marshall, Minn. "You can't stop someone because they're Hispanic."

Immigration and Customs Enforcement spokesman Carl Rusnok in Dallas said agents "always try to respond nationwide when we gets calls from local law enforcement."

But he said in ticketing situations, local police "routinely don't notify ICE."

"This is not a finger-pointing exercise at all," Rusnok said. "We work extremely hard to support our law enforcement partners."

Both local and state officials agree they cooperative effectively when illegal immigrants are caught committing serious crimes and during workplace sweeps.

Last month's encounter

In mid-January, a sheriff's deputy in Kandiyohi County stopped a van for crossing the center line at 2:23 a.m. A passenger in the van said her name was Alianiss N. Morales -- which authorities have determined was Franco's alias.

The man driving that day, Samuel R. Melendez, was fined $187 after police checked and found he had only an instruction permit and the woman identified as Morales had a state-issued ID card.

In 2006, a woman who told police she was Morales drove over a curb and onto a lawn in Montevideo and was fined $182 for failing to possess a driver's license.

In a letter last week to ICE officials, U.S. Rep. Michele Bachmann called that a "deadly error" and wondered why the woman's immigration status went unchecked.

But ICE officials said Thursday that if a person is using a U.S. citizen's identity, the agency would not have been alerted that she was in the country illegally. Customs officials said that the real Morales was from Puerto Rico, whose native-born residents are U.S. citizens.

"When we encounter people for petty offenses, we have no reason to inquire about it," Montevideo Police Chief Adam Christopher said Thursday. "Our experience is that ICE will not deport for those types of offenses."

In an e-mail Thursday, Bachmann wrote: "This story breaks our hearts. But it must also call us to action. We need to secure our borders and to foster cooperation between local police and federal immigration authorities."

Kandiyohi County Sheriff Dan Hartog said his deputies stop countless vehicles and don't probe immigration status every time.

"Then you get into profile issues. We don't do that," Hartog said. "Unless there is some other indicator that something's not right ... there's no reason to look into it any further."

Police tactics dealing with immigrants have been hotly debated in recent years, with Gov. Tim Pawlenty and Twin Cities police chiefs disagreeing on when it's appropriate to ask about immigration status.

The chiefs and immigration activists argue that immigrants need to feel safe reporting crimes to police without fear of deportation. Pawlenty and others have tried to lift the cities' policies against asking about status during traffic stops.

Illegal immigrant walks

Earlier this week in Marshall, Pedro Diaz-Pineda paid a $332 fine for running a stop light and giving police a fake name. During the traffic stop last week, Diaz-Pineda told authorities he was here illegally from Honduras.

Within 10 minutes of paying his fine on Monday, he walked out of Lyon County District Court, according to the Marshall Independent newspaper.

The prosecutor in the case, Lori Buchheim, did not return phone calls Thursday asking about the case.

In Montevideo, Chief Christopher said: "Certainly, if ICE wants us to call on every single one and wants to come out and get them, we would gladly do it. But that's not how it works."

curt.brown@startribune.com • 612-673-4767 plouwagie@startribune.com • 612-673-7102