Michelle Sigona covers an unimaginable crime in Washington, D.C.: Who would shoot a 20-year-old mother and then leave her infant girl inside a hot car to die?

Young mother Wynetta Wright was discovered shot and killed in May 2011. Several block away, police found an equally tragic and horrific crime scene. As police piece together the clues, they found themselves looking a surprising suspect.

A secret affair. A child out of wedlock. Accusations. Lies. Did it all lead to the murder of mother and child?

Now, speaking out for the first time, a heartbroken grandmother asks: Why?

A security camera captured two people talking for hours during an early morning meeting. It was a preview to a horrendous crime.

One of those people on camera is single mom Wynetta Wright, 20.

Wright dreams of becoming a deputy with the Prince George's County Sheriff's Explorer Program. While Wright advances in the program, she meets a mysterious stranger

"She told me his name was Rich, and he was police officer, but that's all she gave me," said Wyvette Wright, Wynetta's mother.

Richmond Phillips, 39, works undercover for D.C.'s narcotics division. The veteran cop is the mentor Wynetta needs, and the man she desires. But Phillips is married, and Wynetta's affair with the older man is a secret. She became pregnant by him.

Little baby Jaylin's arrival is unplanned. The joy isn't shared by Phillips. He completely disowns Wynetta and his new baby daughter.

Wynetta, just out of her teens, is forced to sue Phillips for support. Wynetta gets a court date and serves Phillips with a summons. The night before the hearing, Phillips reaches out to Wynetta for the first time in months.

"He called her a 122 times that day," said Wyvette Wright.

The following morning Phillips shows up for the custody hearing. But Wynetta and Jaylin are a no-show. After hours of no contact, Wyvette is in a panic. The desperate grandma reports her daughter missing.

After five long days of searching, it's no longer a missing-person case. In the parking lot near a community center park, it becomes a homicide. Insider Wynetta's SUV, a horrible and heartbreaking sight. Young Jaylin, 11 months old, was found dead, still strapped in her car seat, left to die in searing heat.

Within hours, police make another tragic discovery in the woods nearby. It's the body of Wynetta Wright. She was shot to death.

Right away suspicions fall on the baby's own father and defendant in the child support case, Richmond Phillips. But the D.C. police department confirms Phillips was working that night.

But then Wynetta's cousin calls in a tip that blows the lid off Phillips's alibi: Wynetta had told her Phillips wanted to meet about the hearing to see if Wynetta would cancel it.

On a hunch, investigators request surveillance footage from the park not far from where Wynetta's body was found, and the entire crime comes into focus. Phillips is seen at a picnic table on the recording.

Investigators determine Phillips ended his paternity suit with a gunshot to Wynetta's head.

After murdering his ex, cops say Phillips moves her car to a nearby parking lot, leaving his own baby daughter to die a horrible death.

Investigators have seen the crime. Now detectives grill the man they think did it, their fellow cop, Richmond Phillips. For hours, Phillips sweats through an interrogation.

Phillips maintains he hasn't talked to Wynetta in over a year, even feigning disgust that she stood him up at the paternity hearing.

But then detectives drops hard evidence on Phillips. They know Wynetta was going to meet him. Wynetta's phone records show she was at the park. Then, detectives tighten the screws, telling Phillips they have the park's surveillance tape. The detective doesn't get a confession, but he gets enough to lock Phillips up.

Phillips is stripped of his badge and gun and charged with a double-homicide.

After only a few hours of deliberation, the jury's verdict is in: Richmond Phillips is found guilty of murdering his ex-girlfriend and their child.

Phillips is sentenced to two life terms. He'll never again be a free man.