TACOMA – A forensics team has combed over an upstair apartment in Des Moines where two women were raped Monday night.

KING

Police released this sketch of the suspect.

Police say six people were in the house when the masked gunman knocked on the door and forced his way into the apartment around 9:30 p.m.

It is the latest incident in a string of brazen attacks and now police from four different departments are investigating if they are all the work of a serial rapist, responsible for as many as four rapes since August.

Police say the serial rapist is described as an African-American male in his 30s, about 6 feet tall, weighing around 200 pounds.

In Fircrest on August 31, a 19-year-old girl was raped in her own bedroom. The girl's mother was home, but had no idea an intruder was in the house.

On October 9, two women in Tacoma were tied up in their home while a third was raped.

And just last week in a Federal Way apartment, three men were tied up while two women were raped at gunpoint.

News of the link between these cases did little to calm the fears of Tacoma residents, who are becoming more careful about locking doors.

In north Tacoma, where the second rape took place, it’s a major issue in some community meetings.

The King County Sheriff's Department said the similarities in the first three incidents are undeniable. In each case, the rapist used a gun, entered through an open door or window and stayed for a long time.

In Federal Way, witnesses say a man matching the description of the rapist was going door to doorm pretending to sell newspapers.

Police said they have enough evidence against the suspect but they don't have a DNA match.

A $1,000 reward is being offered in this case. Anyone with information is asked to call CrimeStoppers at 253-591-5959.