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." 
How many churchwomen were there?
slammed head-on into three nuns