Lesbian couple's murder investigation leads back to father

As detectives chased every lead, grieving family members gathered at a candlelight vigil. Was the sadistic killer among them, a wolf in sheep's clothing?

Hundreds of clues, a massive trail of breadcrumbs to follow, caught on video and in the flesh.

But the biggest bombshell was about to drop: The barbaric monster was in plain sight.

Brittney Cosby and Crystal Jackson were both 24 years old, living in Houston, Texas and in love with each other. For two years, life was an upward trajectory for the young couple. Both were ambitious, hard-working and raising Crystal's 5-year-old daughter Zaniah.

Crystal had been raised by her parents, Reverend Ivan and Mary Jackson. Brittney had been raised by her great-grandmother. Her mom Loranda McDonald and dad James Cosby split when she was young. James was back living in the same house.

Brittney and Crystal hoped to move out and get a place of their own. They first needed a car. Pooling their tax refunds they finally bought a 2006 Kia Sorento with Brittney's great-grandmother co-signing. A few days later, they went over to Crystal's parents' house to pick up Zaniah and show off their new purchase.

As they drove off that night, little did the Jacksons know that would be the last time they'd see their daughter Crystal and her girlfriend Brittney alive.

As worry grew at the Jackson house, about an hour and a half away, in Port Bolivar, an unincorporated community in Galveston County, a delivery driver stumbled upon an unbelievably horrific scene.

"A beer delivery driver was at the convenience store and went to throw boxes in a Dumpster, when he came back in he asked the clerk if they had thrown out mannequins. She went to look and that's when they realized there were actual bodies," said William Kilburn, former forensics investigator for the Galveston County Sheriff's Office. The bodies were found intertwined and strewn like ragdolls Even veteran investigators were stunned at the sheer brutality.

Who could have committed such a horrendous act? One woman was found face-up, eyes open, with a severe wound to the head, a visible gunshot wound. The other woman was found lying on her stomach, severely beaten. A bed sheet was wrapped around her head. As cops pull it back, they see the results of the brutal beating.

Speculation swirled. Was it a hate crime? Or a crime of passion at the hands of a former lover?

Investigators quickly surmised the women were killed at another location and dumped in Port Bolivar. But where were they killed?

Detectives scrutinized the scene, finding three blood spattered wood boards and a bloodstained envelope. On that envelope, an address: Howcher Street in Houston, and the name Brittney Cosby.

At the Houston address, investigators inform Brittney's 90-year-old great-grandmother, Annie Lee Cosby, and her father, James Cosby, of her tragic demise. And they quickly learned the other woman's identity: Crystal Jackson.

Investigators working around the clock caught a much-needed break. A man found a wallet on a dirt road and notified the sheriff's department. It was Brittney's. Investigators theorized that the dirt road close to Brittney's house may have been the first intended dump site.

Two days later they talked again with Brittney's father, James Cosby, hoping to clarify the timeline.

Detectives were puzzled. Why did the women leave that morning without taking Crystal's daughter Zaniah to school?

Detectives believed one of the keys to finding Brittney and Crystal's killer was finding their SUV. Surveillance video from the Galveston Ferry landing showed that around 9 that night, a man was stopped by ferry security in an SUV believed to match the ladies' Kia Sorento. Investigators believed Brittney and Crystal's bodies were in the back of that SUV at the time.

The security guard does offer up a strong description leading to a composite sketch.

Six days after the murders, a fingerprint found at the site where the bodies were dumped came back with a match. That lone fingerprint is a perfect match to Britney's own father.

It was a stunning realization. The man detectives had only seen as the grieving father was now their prime suspect.

With a search warrant in hand, investigators bring a forensics team to the house.

Outside, under the carport blood spots were found, and a missing shutter which matched one found with the bodies.

"His bedroom is adjacent to that carport," said investigator William Kilburn. "On the outside of the house there was false shutters on the main windows, which one was missing. That shutter was found in Port Bolivar with the bodies."

Just inside the door, in the den where James Cosby slept, signs of a bloodbath.

"Everywhere we were looking we were finding something with blood on it," said investigator William Kilburn. "Tiny drops, bigger drops. Pools, swipe marks, they were on the door, in the carpet, in the couch, on clothes."

And when investigators spray the room with chemicals to detect human blood invisible to the naked eye, the room lit up.

Detectives also uncovered a box of bullets with a mix of .38 and .357 shells. They believed the murder weapon was a .357 and the bullet that killed Crystal was a .38.

"This is the most evidence I've ever collected on a crime scene," said Kilburn. "Three hundred and seven individual pieces, and 290 of them said it was James Cosby that committed the crime."

Meanwhile, at a community vigil for Brittney and Crystal, James Cosby pleads for the public's help in finding the killer.

"They ended up picking him up at the vigil," said Kilburn.

Based on all the evidence collected, detectives deduced that sometime in the early-morning hours, as Crystal's daughter sat in the car waiting to be taken to school, James got into a fight with Brittney, savagely beating her to death. They believed Crystal walked in while it was happening and he shot her. Zaniah wandered back into the house from the car, staying with the dead women for hours. James Cosby then spent the day with his girlfriend, and at some point James put Brittney and Crystal in the back of their own SUV and drove to Port Bolivar, where he dumped their bodies.

James Cosby was no stranger to an interrogation room. He'd been in and out of prison for most of Brittney's young life. The last time was for failing to register as a sex-offender.

After Cosby is advised of his rights, an aggressive and stunning five-and-a-half-hour cat-and-mouse game begins.

Investigators confront Cosby with the mountain of evidence against him, like his fingerprint on a piece of paper stuck to one of the boards found with the bodies. Cosby doesn't seem to have much of an explanation for his blood-soaked room.

More than five hours in, James Cosby was arrested. Cops charged Cosby with two counts of tampering with evidence -- all they could hold him on at the time.

Cosby wouldn't crack, but soon a confession would be irrelevant. Just one month later, crystal and Brittney's SUV was found. Inside, more damning evidence: a bullet and a ton of blood.

One year later, James Cosby was charged with capital murder.

Grief-stricken family members were horrified, even as they united to find the killer. He was right under their nose.

James Cosby went on trial, and after three hours of deliberations the jury found him guilty of capital murder. He was sentenced to life without parole.