Ellen Goldberg, NBC 5 News
Some Delta Sigma Thetas are angry after learning that police have suspected for months that a man is targeting members of their sorority.
Plano police are fending off criticism that they should have gone public sooner about a possible serial rapist targeting alumnae of Delta Sigma Theta sorority.
Authorities knew in April that there could be a serial rapist but never alerted the public.
Two women have been assaulted since then.
"I know they're frustrated," Plano police spokesman David Tilley said. "I understand their frustration. We're frustrated, too. I know there have been questions of whether we're doing enough."
Cheryl Smith, a longtime Delta and Dallas talk show host, is among the more vocal critics of how police have handled the case.
"How many women have to be raped -- how many Deltas have to be raped -- before the alarm is sounded?" she said. "Anytime there is someone out there attacking someone, we need to know."
The first attack, an attempted sexual assault, occurred Nov. 2, 2010, in Plano. There was a second attack in April, and police started to connect the dots.
"Telling us in April might have kept there from being another assault," Smith said.
In June, police released a video of the man believed to be assaulting the women. But investigators did not mention that the man was also wanted in the November attack.
Police said they believe the man attacked a third victim in Coppell in September, and a fourth victim was assaulted in Shady Shores two weeks ago.
"You don't want to make any assumptions," Tilley said. "We didn't have any evidence at this point to support that these two were definitely linked. At this point, it was, 'Could it be coincidental? Yes.' It wasn't until after the September and October offenses came forward that these started getting beyond a coincidence."
Tilley said Plano police have met with Delta Sigma Theta's alumnae group three times to discuss the case, including a meeting Oct. 20 when members were warned not to display their Greek letters and sorority colors.
"I hear folks saying, 'Take your tags off, don't wear red and white, don't wear Delta symbols,'" Smith said. "I worked hard for my Delta symbols, and I am going to continue to work and support the organization."
Police said they do not know a specific motive for the attacks but say the man likely cases each of his victims before attacking.
"As time goes on, and the perpetrator is not caught, the fear increases, because you wonder, 'Is this going to happen again? And is it going to happen to me?'" Tilley said.
Investigators would not confirm if they have DNA evidence but say there is physical evidence that police believe will link the attacks.
NBC 5's Kristi Nelson and Ellen Goldberg contributed to this report.