By day Luis Zambrano is a construction worker, but by night police say he's a sexual predator stalking intoxicated women in nightclubs.

At the trendy Manhattan club Marquee, Zambrano was caught on surveillance tape accosting a 23-year-old woman who had passed out on a couch.  

Surveillance video shows that she woke up and tried to fight him off.  But he didn't give up.  As he dragged her limp body out of the bar, she fell to the floor, all the time no one coming to her aide.

Then he dragged her down a flight of stairs.  The video shows him lifting her into his arms, and carrying her out of the night club.  Once again, nobody stopped him.

According to police, he took her to his home and raped her.  Zambrano pled guilty to attempted kidnap and attempted rape.

Experts say it's not unusual for young women to let their guards down during a night out at the clubs, where the partying doesn't start until midnight and goes on for hours.

"It's always fun...The music, the dancing, the people," says one club-goer. "Everyone wants to be part of the nightlife in New York," says another.

But when the clubs close, you often see women stumbling onto the street, trying to figure out how they'll get home.  Some are barely able to stand.  Others are passed out.  And some may never make it home.
 
In just a two-year period, three women were murdered after nights out at New York City nightclubs.

And 26-year-old Laura Garza, an aspiring dancer, has been missing since December.

Police say Laura Garza was last seen leaving Marquee, the same nightclub where the surveillance video of Zambrano was taken.  She left with a man she had just met, 23-year old Michael Mele.

It's unlikely he told her he was a registered sex offender.  Although Mele has denied any role in her disappearance, Laura's cousin told INSIDE EDITION she doesn't believe him.

"Heaven knows if she was under the influence of something he had given her," she says.

Accepting drinks from strangers is one of the many dangers that experts say women should be aware of. 

"Anybody that brings a drink that you haven't seen poured, that wasn't given directly to you by the bartender, never accept it," says safety expert Steve Kardian.

But that's exactly what happened when INSIDE EDITION sent Kardian with hidden cameras into a trendy New York City nightclub.  

In just one hour, five different women gladly accepted a drink from him, a complete stranger.  The drinks could easily have been spiked with a date rape drug.

"It was very easy, too easy.  They had no idea what they were getting into, what they were drinking or what I gave them," Kardian tells INSIDE EDITION's Chief Investigative Correspondent Matt Meagher.

Another huge risk women take is when they separate from their friends. That's something INSIDE EDITION's cameras saw happening over and over again.

"It's very dangerous.  The girls should have a group concept.  You go out as a group, you go home as a group," Kardian says.

When two women, Kim and Allison, working undercover for INSIDE EDITION left a nightclub together, they heard the typical come-ons.  

But when Kim left a night club alone, something more alarming happens.

She is immediately approached by two men who want to give her cocaine, get her in their car and take her home.

"You won't even try a little bit?" asks one man.  "We can go back to my apartment."

"I don't know what they were going to do if I had gone with them, and that's the scary part," says Kim.

Assistant District Attorney Lisa Friel, the Chief of the Sex Crimes Unit for the Manhattan District Attorney, says she sees these kinds of cases every week.

"Women who go out and drink just need to remember there are people looking for them to get inebriated. These people are in the clubs, they're outside on the streets, they're waiting for you to come out," she says.

INSIDE EDITION conducted a survey of 200 young women who were out at nightclubs and 42% told us they've felt threatened by men in clubs. 

To view the full survey results, click Download a PDF at the top of this story.

For nightclub safety tips from ADA Lisa Friel, click here.

Luis Zambrano was convicted of attempted kidnapping and attempted rape and is now serving a three-and-a-half-year prison sentence.