BROWNSVILLE, Texas -- The families of two U.S. immigration agents shot more than a year ago on a Mexican highway renewed their demand Friday that the U.S. government explain the decisions that put them there and answer questions about how guns purchased in the U.S. fell into the hands of their attackers.

The parents of slain Immigration and Customs Enforcement agent Jaime Zapata joined with the sister of agent Victor Avila to press the government on whether an operation similar to one in Arizona that allowed illegally purchased guns to be smuggled into Mexico in hopes to tracking them to higher-ranking criminal figures was responsible for the guns used in the attack. Two of the weapons have been traced to illegal purchases in Texas.

The families spoke in Zapata's hometown of Brownsville, one day after the U.S. House voted to hold Attorney General Eric Holder in contempt for not providing documents relevant to an investigation of so-called Operation Fast and Furious in Arizona. In that case, agents with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives lost track of hundreds of weapons they had hoped to trace higher in criminal organizations. Justice Department policy had long forbid such "gun walking" and two guns from that operation were found at the scene of the slaying of U.S. border agent Brian Terry.

"I feel that I owe my son justice and I still haven't gotten it," said Mary Zapata, the slain agent's mother, wearing a lapel pin with her son's picture.

Earlier this month, Zapata's family filed a $25 million wrongful death claim against the U.S. government. Avila is seeking $12.5 million claiming negligence and intentional infliction of emotional distress. The claims are an initial step toward lawsuits. They note that at least two weapons used in the attacks originated in Texas and were passed to cartel gunmen in Mexico by known gun runners in the U.S.

"I do believe that guns that were walked through the Dallas area especially were responsible," said Mary Zapata.

Tom Crowley, a spokesman for the Dallas field division of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, said the agency "has always said that this investigation has no connection whatsoever to Fast and Furious."

Crowley denied the agency knew about the Dallas-area gun purchase beforehand.

"We had no knowledge of the Oct. 10, 2010, purchase of that weapon prior to the transaction; we had no idea the transaction was going down," said Crowley.

Zapata and Avila were on their way back to Mexico City on Feb. 15, 2011, after meeting a colleague in San Luis Potosi to pick up equipment. They were driving an armored black Chevrolet Suburban when two SUVs carrying gunmen ran them off the road. Once they placed the Suburban in park, the door locks automatically opened. In the struggle to close the door, a window was opened and shots were fired into the vehicle, killing Zapata and wounding Avila.

People involved in the illegal purchase of the guns used in the attack have been convicted in U.S. courts. One person allegedly involved in the attack, Julian Zapata Espinoza, has been extradited to the U.S. and awaits trial in Washington, D.C., on murder charges.

Attorneys for both families say the U.S. government has told them little since the days immediately following the attack. Trey Martinez, one of the lawyers, said some of the outstanding questions include why the agents were on the road after sharing their safety concerns with superiors; whether superiors were aware of a flaw in the armored vehicle that automatically unlocked the doors; and why an alternative diplomatic service wasn't used to transfer the equipment.

Magdalena Villalobos said her brother's physical wounds have healed, but he is still recovering emotionally from the attack during which 90 shots were fired into the vehicle. She said her brother is receiving treatment to move past it.

"Being there when Jaime expired has been an incredibly difficult thing for him to try to wrap his mind around," she said.

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Associated Press writer Pete Yost in Washington, D.C. contributed to this report.

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10 Major U.S. Federal Laws
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  • The Naturalization Act of 1790

    The Naturalization Act of 1790 was our country's first set of laws dealing with citizenship. Applicants had to be "<a href="http://rs6.loc.gov/cgi-bin/ampage?collId=llsl&fileName=001/llsl001.db&recNum=226 " target="_hplink">a free white person</a>" of "good moral character." This excluded indentured servants and slaves. Good moral character was substantiated by establishing residence for at least one year in the state from where he was applying, and at least two years of residence in the country. The Naturalization Act of 1795 would extend that requirement to five years, and is still standard today.

  • The Fourteenth Amendment, 1868

    A Reconstruction Amendment that was added to the U.S. Constitution following the Civil War, the Citizenship Clause of the 14th Amendment establishes for the first time that children born on U.S. soil would be conferred U.S. citizenship regardless of their parent's citizenship status, race, or place of birth. Last year, Rep. Steve King (R-IA) introduced the <a href="http://www.govtrack.us/congress/bills/112/hr140 " target="_hplink">Birthright Citizenship Act of 2011</a> to Congress, and challenged this. The bill would require that at least one parent be a U.S. citizen or permanent resident for a child to be granted citizenship. According to the <a href="http://www.opencongress.org/bill/112-h140/text " target="_hplink">bill's text</a>, the Birthright Citizenship Act of 2011 would amend the Immigration and Nationality Act of 1952, and "clarify those classes of individuals born in the United States who are nationals and citizens of the United States at birth." Prior to this, Rep. Nathan Deal (R-GA) <a href="http://www.huffingtonpost.com/2009/05/26/nathan-deal-georgia-lawma_n_207485.html " target="_hplink">introduced</a> a similar <a href="http://www.opencongress.org/bill/111-h1868/show" target="_hplink">bill</a> in 2009.

  • The Naturalization Act of 1870

    The Naturalization Act of 1870<a href="http://thepoliticsofimmigration.org/pages/chronology.htm " target="_hplink"> explicitly extended</a> naturalization laws to "aliens of African nativity and persons of African descent." This meant that for the first time, African-American children would be conferred citizenship upon birth. Asian immigrants and other people of color are excluded per the Naturalization Acts of 1790 and 1795.

  • The Page Act of 1875

    Named after Republican Representative Horace F. Page, this is the first U.S. federal immigration law to explicitly prohibit the immigration of a particular group: persons of Asian descent. Primarily meant to limit Chinese immigrant labor and prostitution, the Page Act prohibited the immigration of: (1) contracted labor from "China, Japan, or any Oriental country" that was not "free and voluntary," (2) Chinese prostitution and (3) criminals and women who would engage in prostitution. Ultimately, the <a href="http://www.uchastings.edu/racism-race/pageact.html " target="_hplink">Page Act</a> severely <a href="http://immigration-online.org/228-page-act-united-states-1875.html " target="_hplink">restricted</a> the immigration of Asian women. Only 136 of the the nearly 40,000 Chinese immigrants who arrived in the months before the bill's enforcement were women. And, it would pave the way for the Chinese Exclusion Act. In this picture, Michael Lin, chair of the 1882 Project, a coalition of rights groups seeking a statement of regret over that year's Chinese Exclusion Act, speaks on May 26, 2011 in Washington, DC, at the US House of Representatives in front of a reproduction of a 19th-century sign that aimed at rousing up sentiment against Chinese Americans. Lawmakers introduced a bill that would offer an official statement of regret for the act, which banned further immigration of Chinese to the United States and ended citizenship rights for ethnic Chinese. (AFP PHOTO/SHAUN TANDON).

  • The Chinese Exclusion Act, 1882

    Signed by President Chester A. Arthur, the <a href="http://www.pbs.org/weta/thewest/resources/archives/seven/chinxact.htm " target="_hplink">Chinese Exclusion Act</a> was the first federal immigration law to prohibit immigration on the basis of race. The bill barred all Chinese laborers, skilled and unskilled, from immigrating to the U.S. for ten years. It was made permanent by 1903, and was not lifted until the 1943 Magnuson Act. The 1898 Supreme Court <a href="http://ocp.hul.harvard.edu/immigration/exclusion.html " target="_hplink">decision</a> in <em>United States v. Wong Kim Ark</em> finally extended naturalization laws to persons of Chinese descent by ruling that anyone born in the United States was indeed a U.S. citizen. This editorial cartoon from 1882 shows a Chinese man being excluded from entry to the "Golden Gate of Liberty." The sign next to the iron door reads, "Notice--Communist, Nihilist, Socialist, Fenian & Hoodlum welcome. But no admittance to Chinamen." At the bottom, the caption reads, "THE ONLY ONE BARRED OUT. Enlightened American Statesman--'We must draw the line <em>somewhere</em>, you know.'" (Image Source: Frank Leslie's illustrated newspaper, vol. 54 (1882 April 1), p. 96. [Public domain], via <a href="http://commons.wikimedia.org/wiki/File:The_only_one_barred_out_cph.3b48680.jpg" target="_hplink">Wikimedia Commons</a>).

  • The Naturalization Act of 1906

    The Naturalization Act of 1906 further <a href="http://www.understandingrace.org/history/gov/eastern_southern_immigration.html" target="_hplink">defined</a> the naturalization process: the ability to speak English was made a <a href="http://www.enotes.com/topic/Naturalization_Act_of_1906" target="_hplink">requisite</a> for immigrants to adjust their status.

  • The Immigration Act of 1924

    U.S. President Coolidge signed this U.S. federal <a href="http://history.state.gov/milestones/1921-1936/ImmigrationAct " target="_hplink">bill</a> into law. It capped the number of immigrants who could be admitted entry to the U.S. and barred immigration of persons who were not eligible for naturalization. And, as the Naturalization Act of 1790 required, an immigrant had to be white in order to naturalize. The quotas varied by country. Image Source: Flickr Creative Commons, <a href="http://www.flickr.com/photos/nycmarines/6306315902/" target="_hplink">NYCMarines</a>.

  • The Immigration and Nationality Act of 1952 (The McCarran-Walter Act)

    The <a href="https://docs.google.com/viewer?a=v&q=cache:zwaVG82lZisJ:www-rohan.sdsu.edu/dept/polsciwb/brianl/docs/1952McCarranWaltersAct.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEESjEwx76FIBTixZAfyncZz-1CSuSeciv5qB6vvWTrUfW58XRpXq8zkpnI57XSuuG5Bu-WSySGbEhxYvZxP7y6qDQuOsDhgDa6qUqUaJ8F4imTzKJsVtppHc_-eew2dK6vGhoIUZs&sig=AHIEtbTNQ5GFiNMVS-xyThq8VVSj_gG9KA " target="_hplink">McCarran-Walter Act</a> kept up the controversial Immigration Act of 1924, but <a href="http://history.state.gov/milestones/1945-1952/ImmigrationAct" target="_hplink">formally</a> ended Asian exclusion.

  • Immigration and Nationality Act of 1965

    When President Lyndon Johnson signed the Immigration and Nationality Act of 1965, it <a href="http://library.uwb.edu/guides/USimmigration/1965_immigration_and_nationality_act.html" target="_hplink">abolished</a> the quota system that favored immigration from Europe and limited immigration from Asia and South America.

  • Illegal Immigration Reform and Immigrant Responsibility Act of 1996

    The 1996 <a href="http://www.uscis.gov/ilink/docView/PUBLAW/HTML/PUBLAW/0-0-0-10948.html " target="_hplink">Illegal Immigration Reform and Immigrant Responsibility Act</a> (IIRIRA) is a piece of legislation that <a href="http://library.uwb.edu/guides/usimmigration/1996_illegal_immigration_reform_and_immigrant_responsibility_act.html " target="_hplink">defined</a> an array of issues to do with legal and illegal immigration -- from outlining how border patrol agents should administer visa processing, to the minutiae of how to handle deportation proceedings -- IIRIRA established enforcement and patrolling practices.