Federal immigration officials let thousands of inmates in the nation's third-most populous county walk out of jail despite the suspects admitting they were in the U.S. illegally, a newspaper investigation found.

More than 3,500 inmates told Harris County jailers they were in the country illegally over an eight-month period starting in June 2007, but records show Immigration and Customs Enforcement filed paperwork to detain only about a quarter of them.

In a story published Sunday, The Houston Chronicle found that most illegal immigrants released from jail were accused of minor crimes. But others included convicted child molesters, rapists and those ordered to be deported decades ago.

ICE officials said they are doing the best they can with their resources.

"No agency has enough law enforcement officers to do the job the way they'd like," Kenneth Landgrebe, ICE's field office director for detention and removal in Houston, told the Chronicle.

The Houston ICE office set a record by removing 8,226 illegal immigrants with criminal records from southeast Texas last year, an increase of about 7.5 percent from fiscal year 2007.

ICE officials said between 300,000 and 450,000 inmates incarcerated in the U.S. are eligible for deportation each year. The agency estimates it screens inmates in only about 10 percent of the nation's jails.