Raleigh, N.C. — Less than a day after a pregnant mother was found murdered behind a Raleigh convenience store, police said they received a mysterious phone call that could provide a lead in the case.

Police also released a composite sketch late Friday of a man they want to question in the case.

An officer responding to a report of a suspicious vehicle found the body of Jennifer Kathleen "Jenna" Nielsen, 22, of Fuquay-Varina, behind the AmeriKing Food Mart on Lake Wheeler Road, across from the State Farmers Market, early Thursday morning.

Nielsen, the mother of two boys who was eight months pregnant with her third son, was on her early morning route to restock USA Today newspaper boxes when she was killed, police said. The cause of death hasn't been released.

At about 1:30 a.m. Friday, a Spanish-speaking man called 911 dispatchers from a pay phone near the intersection of South Saunders and West South streets and said he had information related to Nielsen's death, said Jim Sughrue, spokesman for the Raleigh Police Department.

The caller quickly hung up, but investigators went to the phone booth and checked it for fingerprints and other clues, Sughrue said.

Police described the slaying as a random act and said they want to identify a man seen near the convenience store in the pre-dawn hours Thursday.

The man is described as being in the late teens or early 20s, standing about 5 feet, 3 inches tall and weighing about 120 pounds. The man had black hair pulled into a ponytail and wore a dark-colored sleeveless shirt and baggy denim shorts.

Anyone familiar with the man is asked to call the Raleigh Police Department. A special telephone line at 919-227-6220 has been dedicated to receive tips about the crime.

A reward will be available for information that assists the investigation.

Nielsen's family said all they want is justice in the case.

"This person murdered a pregnant woman with a child inside of her," said her husband, Tim Nielsen. "This person killed two people."

Her 3-year-old son, Schyler, wants to know where his mother in, said her brother, Jason Kubota.

"He keeps saying, 'Mommy. Mommy's come home,' you know. And we say, 'No, Mommy's not coming home,'" Kubota said.

"They're not going to ever see their mommy again," Tim Neilsen said of his sons. "We're going to keep going. I mean, we really have no other choice."

As they planned funerals in Utah for both Jennifer Nielsen and her unborn son, relatives asked for anyone with information about the slaying to come forward.

"People might have seen somebody leave, somebody come by," Kubota said.