Randy McIlwain, NBC 5 News
Police now believe the man who sexually assaulted members of the Delta Sigma Theta sorority lives in the Mesquite area.
Police said the man who has sexually assaulted members of a national black sorority could live in the Mesquite area.
The serial rapist has attacked at least four alumnae of Delta Sigma Theta in three North Texas cities and towns.
Police said they have a DNA profile of the man.
Investigators said Monday that the man used a convenience store pay phone to call and check on one of his victims after the April attack.
"Our victim actually received a phone call from the suspect," Plano police spokesman David Tilley said. "He was just basically checking on her welfare, making sure that she was OK, even though that may sound odd."
The victim does not know the man, police said.
Police previously released surveillance footage of the man from the convenience store.
Tilley said the man was talkative with his victims and had specific information about each of them, including phone numbers and addresses.
"He does have a lot of specific information related to each of these victims that we're really not sure where he's getting it from," he said.
Each attack involved a home invasion. Unlike most non-acquaintance rapes, the man did not beat or threaten to kill his victims, Tilley said.
"Initially, from the outset, [he said] he didn't want to hurt them, and he wouldn't hurt them as long as they cooperated," he said.
Tilley said people in the Mesquite area who know the attacker might not realize it because they think they are too far away from Plano, Coppell and Corinth or because his mannerisms are of a calm, nonviolent person.
"I think a lot of people, I would say, have pictured this guy as being a violent monster -- and I understand that, totally -- whereas, in fact, what we're dealing with is a guy who from the get-go has said he was not going to harm them, as long as they cooperated, they would not be harmed."
Tilley said investigators do not know if the man lives or works in Mesquite or was visiting when he made the call to the victim.
"This is a sick individual," he said. "This is somebody we need to be concerned about."
"These victims have been through a horrific crime, and this guy is not behind bars, and we need to put him behind bars, and we're asking for the public's help in trying to do this, because it's not going to be until then that these women can walk out of their house and feel like they're safe," Tilley said.
Police released a written timeline of the attacks and additional details about the surveillance video from Mesquite.
November 2010 -- Attempted sexual assault reported in Plano
April 2011 -- Sexual assault reported in Plano
April 2011 -- Plano police detectives meet with sorority alumni members
June 2011 -- Press release and surveillance video / photos released by Plano Police Department
September 2011 -- Sexual assault reported in Coppell
October 2011 -- Sexual assault reported in Shady Shores
October 2011 -- Detectives from Plano, Coppell, and Corinth police departments meet again with sorority alumnae members
October 2011 -- Press release and surveillance video / photos re-released by Plano Police Department
October 2011 -- Plano Police Department’s Crime Prevention Unit hosts a personal safety class for sorority alumnae members.
NBC 5's Randy McIlwain contributed to this report.