Bristow, Virginia (CNN) -- Homeland Security Secretary Janet Napolitano has ordered an investigation after a man who was in the United States illegally killed a nun in a car crash, authorities said.
Napolitano is trying determine why the man was still in the country because he had been arrested two previous times for drunken driving offenses.
The suspect, Carlos Montano, driving Sunday morning under the influence of alcohol, slammed head-on into three nuns in a Toyota sedan, police said. The three were just a few miles from a monastery in Bristow, Virginia, heading for their annual retreat. Sister Denise Mosier was killed instantly, and the other two remained hospitalized Tuesday.
The suspect has twice been in custody -- the first time, almost two years ago in October 2008 -- Immigration and Customs Enforcement officials said. But both times, Montano was released on his own recognizance pending deportation proceedings, because he was not convicted of a violent felony such as murder, rape, or robbery.
"He was in removal proceedings," Napolitano told CNN on Tuesday. "Why were the removal proceedings taking so long? I do not obviously as of today have the results of that, but I will get them."
Corey Stewart, chairman of the Prince William County Board of Supervisors, said he was furious with how immigration officials have handled the case.
"We identified him as an illegal alien, we told ICE that he had twice been convicted now of DUI's, that he posed a threat to the community," said Stewart. "And they turned around and they released him right back into the neighborhood."
County prosecutor Paul Ebert said Montano has previously been convicted twice for drunken driving, as well as reckless driving, speeding, and public drunkenness. He spent 20 days in jail in 2009.
The suspect, 23, has now been charged with involuntary manslaughter. It was unclear if he has retained a defense lawyer.
The incident comes amid a contentious national debate about illegal immigration, just days after a strict new immigration law was scheduled to go into effect in Arizona. The most controversial provisions of the law have been stayed by a judge, but supporters of the law said a failure by Washington to crack down on illegal immigration forced Arizona to act.
The Department of Homeland Security says record numbers of immigrants who have committed crimes have been removed in the last 18 months.
"This administration has fundamentally reformed immigration enforcement," said spokesman Matt Chandler, "identifying and removing criminal aliens who pose a threat to public safety."
But Stewart said more needs to be done.
"Congress has deliberately understaffed and underfunded immigration enforcement for years," Stewart said.
On Tuesday, the Virginia monastery's chapel was adorned with flowers, and a vigil and funeral are scheduled for later this week.
Mosier, the victim in the car accident, had served as a missionary in South Africa, and regularly acted as a spiritual mentor to the 30 other nuns at the convent.
"It's a great loss, because they depended on her," said Sister Andrea Verchuck.
But the convent said in a statement, "The Benedictine Sisters are dismayed and saddened that this tragedy has been politicized, and become an apparent forum for the illegal immigration agenda."
Verchuck said she would rather focus on the needless tragedies caused by drinking and driving, and on forgiveness, in memory of Mosier.
"If she had been conscious at the time that she was taken from the wreck," she said, "If Carlos had been there, she would have said, 'Carlos, I forgive you.' "
CNN's Rachel Streitfeld contributed to this report.