(Image Source: ABC News/Plano, Texas, {Police Department) 

BY KYLIE MCGIVERN

The common bloodline of sorority sisterhood flows through the veins of a serial rapist case in Texas. KXAN has more on attacks that media across the country are calling “chilling.”

Reporter: “Investigators in north Texas have released this surveillance video as they continue to search for a serial rapist, who’s attacked at least four alumni members of the Delta Sigma Theta Sorority.”
Police Officer: “All of our victims have been black females, age ranges from mid-50s to mid-60s.”
Reporter: “And all home alone in their upscale suburban Dallas neighborhoods at the time of the assaults.”
Police Officer: “He kicked the door. No other knocking, no other warning.”

The four women were raped within the past 11 months - the most recent attack just last Friday. Police say the similarities are too striking to be coincidence.  
ABC News spoke with a criminal profiler, who says the motivation behind this rapist’s actions-- is hard to pin.

Criminal Profiler: “This is a very unusual rapist, because rapists usually don’t target specific people for any particular reason. They usually find victims that are just in their neighborhood, that are convenient.”
Reporter: “Police aren’t sure how he’s choosing his victims, but the sorority’s national headquarters in Washington isn’t taking any chances, warning north Texas women not to their their Greek letters, and to remove key chains and bumper stickers.”

Police are also telling Delta Sigma Theta sorority members to take down any postings or personal information about themselves from social networking sites.
MSNBC reports why.

Tameron Hall:“Police are saying the man let the victims, or indicated to the victims, he knew personal details about them - that he may have been stalking them.”
Reporter: “Yeah, and that’s another frightening aspect of this case. He apparently knew intimate, personal details about each of the women involved.”

Finally, the Daily Mail quotes a forensic psychology professor from John Jay College of Criminal Justice in New York, who says -- no doubt about it. There’s a reason these women were targeted.

John Jay College of Criminal Justice in New York Forensic Psychology Professor:
“It certainly sounds like he has some beef with that sorority. It’s very hard to know if this is from 30 years ago, if this is from now, if this is a revenge thing... Maybe it’s just his bizarre way to target women for some reason. There’s a common thread in these sorority sisters, these grown-up sorority sisters, that perhaps makes them vulnerable in his mind or desirable for his purposes.”

Police have requested for two local alumni chapters to provide rosters of past and current members of the sorority as the investigation continues.