(Plano, Texas, Police Department)

Police in the Dallas area are hunting a suspected serial rapist who appears to be targeting alumnae members of one sorority, and each of the victims told investigators the assailant seemed to have personal knowledge about them.

Four alumnae of the same sorority — black women in their mid-50s to early 60s — were raped in their Dallas-area homes over the last 11 months, apparently all by the same assailant, according to an alert sent out by the Plano, Texas, Police Department.

The most recent of the attacks occurred around 9:15 p.m. Friday in Corinth, police said.

The police statement did not identify the sorority, but the Dallas Morning News reported that it was Delta Sigma Theta, and that the sorority had sent out email alerts to alumnae.

Some alumnae of the sorority told ABC News that they themselves had not received the email alerts, but said they had heard about them from others.

Besides the attack in Corinth, in  Denton County, two of the rapes occurred in Plano and other in Coppell, both of which are in Dallas County.

The suspect, who is seen in a surveillance video released by the Plano police, is described as a black man, estimated to be in his late 30s to mid-40s, 5 feet seven inches to 6 feet tall and 250 to 300 pounds. He has a trimmed beard and short hair, and possibly a receding hairline, police said.

Each of the four attacks happened between 9 p.m. and 4 a.m. According to the Morning News the alerts also advised that police have requested a full list of each chapter’s members.

“I am sure this is alarming and the area DFW Chapter presidents have received many phone calls in reference to these incidents,” the email said. “Our National President, National First Vice President and Regional Director are aggressively gathering information to distribute to the chapters.”