Left: Hofstra University students mourn Andrea Rebello during a vigil...

Left: Hofstra University students mourn Andrea Rebello during a vigil held May 18, 2013 at the Hempstead school. Right: Hofstra University junior Andrea Rebello, 21, was killed during an armed home invasion at an off-campus residence in Uniondale. This photo is from her blog, http://andrearebello.wordpress.com. Credit: Danielle Finkelstein / Handout

Jessica Rebello is haunted by thoughts of what she might have done to prevent the death of her twin sister, Andrea, the 21-year-old Hofstra University student shot by a Nassau County police officer during a home invasion last week.

On Monday, Andrea Rebello's godfather, Henrique Santos of Eastchester, said Jessica was "devastated," too distraught to eat and sleeping much of the time. While Jessica doesn't blame herself, he said, she keeps asking if she could have somehow prevented the tragedy.

"When she wakes up, she says 'Oh my God, what did I do wrong?'" Santos said, standing outside the Rebellos' Altamount Street home in Tarrytown.

Jessica and the rest of the family keep replaying the circumstances surrounding the shooting in their minds, Santos said.

The siblings, who were very close, lived in the same house near Hofstra on Long Island and were together in the early hours of May 17 when suspected armed robber Dalton Smith, 30, broke into the home and held Andrea at gunpoint. There was another unnamed woman and Jessica's boyfriend in the residence at the time, officials said.

Police were responding to a 911 call on the robbery when veteran police officer Nikolas Budimlic shot Andrea and Smith, killing both, sources said. Police did not name the officer, but sources confirmed that it's Budimlic, who has been placed on sick leave and could not be reached for comment.

Santos, however, didn't have kind words for the officer.

"I think the police is not very professional," Santos said. "If he's professional, he should have tried negotiation."

POLICE TAKEN OFF GUARD

Nassau police and the district attorney's office continue to investigate the chaotic and fast-moving home invasion and what occurred between the time dispatchers sent out the call and six minutes later, when the shots were fired.

Several questions remain unanswered: Were police procedures followed? Did one of the hostages, sent by Smith to get money from an ATM, mention hostages in the 911 call? Did dispatchers inform officers of a possible hostage situation?

Police Inspector Kenneth Lack said "it does not appear that he (Budimlic) knew" hostages were being held. A source in the district attorney's office said there was no evidence that Budimlic deviated grossly from police protocol.

"If he knew there was a hostage inside, he wouldn't have gone in when he did," said a Nassau County police source.

Jessica, initially complied with the gunman's order by telling the officer at the door that nothing was wrong, Lack said. "She said it was a sorority house and everything was fine," he added.

Then she screamed "he's got a gun" and ran out of the house. That's when Budimlic entered the residence and a male hostage hiding behind a sofa shouted, "the police are here," officials and sources said.

"The element of surprise was lost" for police, Lack added.

FAMILY PREPARES FOR WAKE TUESDAY

As friends and family dropped off food and flowers at the Rebellos' house Monday, Santos asked journalists waiting outside to speak with the parents, Fernando and Nella Freitas Rebello, to give them privacy as they mourn.

"We are heartbroken and overwhelmingly devastated by the loss of our beautiful daughter, Andrea," he said, reading a prepared statement. "We are grateful for all of the kindness and sympathy shown to our family. In our grief, we ask for privacy as we try to make sense oF all that has happened. Please understand and respect that Andrea's wake and funeral this week is for our family and close friends only."

A wake for the Sleepy Hollow High School graduate, who is of Portuguese descent, will be held Tuesday from 4-8 p.m. at Coffey Funeral Home in Tarrytown. Her funeral is set for Wednesday at 10 a.m. at St. Teresa of Avila Church in Sleepy Hollow. Burial will follow at Sleepy Hollow Cemetery.

The Rev. Osvaldo Franklin, of Our Lady of Fatima in Yonkers, who performs a Mass in Portuguese most Sundays at St. Teresa's, will lead the services.

POLICE: A 'CRIME OF OPPORTUNITY'

As family and friends prepare to say their last goodbyes to Rebello, police said the home invasion appears to have been a "crime of opportunity."

About 2:20 a.m., the Rebello sisters and two others returned to their rented California Avenue in Uniondale, police said. The male occupant went to retrieve his keys from the home's second floor so he could move his vehicle, and left the front door open.

He returned with his keys to find an armed man, identified as Smith, wearing a ski mask. Smith pointed his gun at the man and ordered him to sit on a sofa in the living room, where two female residents already were seated, police said.

Smith demanded money, jewelry and valuables from the residents, and they told him all their belongings were upstairs, police said. Everyone was forced upstairs at gunpoint. The residents handed over a small amount of cash, so Smith demanded to know if anyone had a bank account.

One female resident said she did, and police said Smith told her she could leave the house to withdraw money from a nearby bank. He told her to return within eight minutes or one of her housemates would be shot dead, according to police.

The woman left the home and called 911 on the way to the ATM. When the police arrived at the house, Smith demanded that Jessica answer the door and tell officers that everything was fine, officials said. Jessica initially complied, but then chaos ensued when she fled and her boyfriend shouted, "the police are here."

Police entered the home, according to investigators, and saw Smith order the male occupant onto the floor at gunpoint at the top of the stairs. Smith then pushed him down the stairs and put Andrea into a headlock and walked her down the stairs at gunpoint, police said. He kept her close to his body and tried to escape through a back door, but was confronted by officers.

Smith made a menacing motion and pointed his gun at the officers, prompting them to shoot, police said. A total of eight shots were fired, seven of which struck Smith, killing him. One bullet hit Andrea in the head. She was pronounced dead at a hospital. No one else was injured in the home invasion.

SPLIT-SECOND DECISIONS REQUIRED

A law enforcement expert said the officers were faced with tough life-or-death decisions.

Eugene O'Donnell, a lecturer at John Jay College of Criminal Justice, as well as a former NYPD cop and prosecutor in Queens and Brooklyn, said that in a situation like the Hofstra shooting, officers often are trained to avoid rushing into the home. Instead, they try to buy as much time as possible and call in a negotiator and a specialized unit, he said.

Police are generally trained to "isolate and contain" the suspect to negotiate a peaceful conclusion, he said.

"The ideal situation is everyone stays in one place and more skilled people come in to help," O'Donnell said. "Time is your friend, usually. Lack of time can be deadly. Once you're in the house, that's generally a place you don't want cops to be. You're trying to take a breath and slow down the clock, rather than rush things."

Budimlic is described as a 12-year veteran of the force who previously spent seven or eight years with the New York City Police Department.

Smith had an extensive criminal record, including several robbery arrests dating to 1999, police said. A warrant was issued for Smith in April for violating parole, police said.

With Kevin Deutsch, Anthony DeStefano, and Ann Givens

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