They've been digging on a private property on East Orem Drive and Martindale for more than a week. Authorities say suspect William Reece identified the property.
Reece is in prison on another kidnapping case. But officers have taken him to the site several times to point out places to dig.
Cain was 17 when she disappeared in 1997. We've also learned that detectives from Denton in north Texas were at the dig site last month. That's because Reece is also a person of interest in the disappearance of Kelli Cox, 20.
Cox went missing in Denton in 1997, the same year Cain vanished.
The Denton Police Department issued the following statement:
"The Denton Police Department had an investigator in the Houston area from February 15, 2016 through February 18, 2016. The investigator was working a "cold case" in cooperation with the Texas Rangers. Texas Rangers met with a person of interest in the disappearance of Kelli Cox. Cox went missing in the City of Denton on July 15, 1997. The Denton Police Department is still actively investigating the disappearance of Kelli Cox and will continue until the facts of Kelli Cox's disappearance are known. The Denton Police Department is not able to provide further information at this time."
Reese is a suspect in five kidnapping or murder cases and was convicted in a sixth kidnapping case. That victim escaped.