HOUSTON — The “CSI”-style wizardry increasingly being used to solve crimes is running up against its limitations in Houston, where police are hunting for a possible serial killer in the slayings of seven prostitutes.

The victims’ nude bodies were discovered over the past 22 months, with most of the victims dumped near churches in Acres Homes, a neighborhood where shabby bungalows and gleaming new homes share the same streets.

The slayings have spurred one of the most intensive homicide investigations in Houston history, filling seven 4-inch-thick binders and yielding a 695-page report. But investigators say the hunt has become a roller coaster ride of frustration and 18-hour work days.

The women lived in a shadowy, secretive world, where their final movements are extremely difficult to trace and witnesses reluctant to step forward.

“These girls are working late at night. No one’s out there. There are no witnesses,” said Lt. Ron Walker, who is overseeing the investigation. “They get into a car with a man they don’t know and they end up in a ditch.”

Some of the women could have picked up as many as 10 customers in one night, and several had semen from a number of men on their bodies, making it nearly impossible for police to figure out the last person they were with or to determine if they had been sexually assaulted.

Police are entering the DNA into an FBI database that contains genetic samples from convicted felons and from crime scenes. So far, the database has yielded no suspects, said homicide Capt. Steve Jett.

Some of the DNA on the prostitutes probably belongs to customers who have no criminal record and are not even in the database, investigators said.

“DNA does not come with a driver’s license,” Jett said. “So we are not able to determine exactly who was involved with this person.”

Police have questioned other neighborhood prostitutes, hoping that one of them might remember something useful. Many told of sexual assaults or frightening encounters, but never reported them and couldn’t identify a customer, Walker said.

Ten officers worked full-time on the case at one point, but that has dwindled to three.

“You have no idea how frustrating this whole case is. We get some leads that we think are good, then have to eliminate them,” Walker said.