Monday night at about 9:30, a man knocked on the door of a second floor apartment at the Des Moines Ridge apartment complex on Kent-Des Moines Road.

Police say that when a woman opened the door the attacker put a gun to her head and forced his way into the apartment.

A woman, her two adult daughters, an adult female friend, and two young children were bound and blindfolded.

Police say that over the course of four hours the attacker sexually assaulted two of the adult women, stole money from the apartment, and told the six victims he would kill them if they told police.

"I feel really, really bad for them," said Karen, who lives in the first floor apartment underneath the one where the attack happened. "I wish I would have done something for them but like I said it's like the noise I hear all the time," she said of the noise of someone pacing back and forth in the apartment for several hours Monday night.

The victims say the man wore a dark knit mask. He was described as a black male, six feet tall, 170 pounds with a stocky or medium build, and was wearing dark pants and a multi-colored square pattern wool hunting jacket.

Just hours earlier the King County Sheriff's Office announced they believed that three other recent home invasion rapes were likely committed by the same man.

On August 31st a 19-year-old woman was raped in her home in Fircrest in Pierce County.

On October 9th a man matching the same description forced his way into a North Tacoma home, tied up two women, and raped a third.

On October 27th a man, again with a similar description, broke into an apartment at the Enchanted Woods complex near Federal Way. In that case the rapist tied up three men and sexually assaulted two women. He was in the home for more than 4 hours.

"We do have a very dangerous suspect out there," said King County Sheriff's spokesman John Urquhart. "It certainly appears that we may have the same suspect who committed all three crimes."

Detectives from three agencies were already waiting for forensic evidence to be processed by the Washington State Patrol Crime Lab to confirm if they are hunting for the same serial rapist.

Tuesday night State Patrol investigators were at the Des Moines apartment complex to search for evidence that might link the same man to this fourth attack.

"It's scary to think that happened that close and we didn't hear anything," said neighbor Autumn Kilp. "It's scary to think somebody watches you to know what's going on that would go in there and even do that in front of other people is disgusting and scary. Something's wrong with that person."

If you have information that could help police with this investigation they ask that you call your local police department or 911.

The King County Sheriff's Office tip line is available 24 hours a day at (206) 296-3311.

Crimestoppers is offering a $1,000 reward for information that leads to the arrest and charges filed against the rape suspect or suspects. That number is (253) 591-5959 or 1-800-Crime13.