Her neighbor, Wendy Pursinger, asked why she needed it. Roberts' two children had long outgrown being pushed in a baby carriage.
"I'm pregnant, of course," Roberts told Pursinger.
Police now say Roberts' pregnancy story was likely false, a cover story. The 27-year-old is charged with killing her pregnant friend, Heather Snively, and say she cut open the 21-year-old's abdomen to take her baby and pass it off as her own. Snively's body was found Friday in a crawl space of Roberts' suburban Hillsboro home.
Her infant also died, but authorities couldn't determine whether he was alive when he was removed — a distinction that could mean the difference between holding Roberts responsible for his death or not. Roberts was in court Monday but did not enter a plea to a murder charge in Snively's death.
Robert's story was inconsistent: Sometimes she told people she was pregnant with one baby. Other times it was twins. She even put a crib together on her front lawn and placed an ad on Craigslist looking for baby clothes.
It was on the online classified site where Roberts and the young mother-to-be met a few weeks ago, Snively's family says. Police are trying to confirm that.
The Web site was old hat for Snively.
"Heather's No. 1 thing to do was be on the computer," said Sandy Carson, a neighbor back when Snively was living in Maryland. "She sold so many things off Craigslist."
She also always had her hand on her belly as she waited for the birth of her first son, who she planned to name John Stephen.
"It's just a habit," she told Carson. "I just can't wait to see him."
"I've actually worn out a shirt doing that," she told Carson.
By most accounts, Snively was a naive young woman. "But you couldn't hold that against her," Carson says. "She could make friends with anybody. She was a very trusting person."
Snively came to Oregon in the spring, following her boyfriend, the father of the boy she had been carrying for nearly eight months.
Not long after moving here, Snively and Roberts connected online. Roberts was looking for clothes and Snively had some to trade.
Neighbors say they saw the two women at Roberts' house more than a couple times during the past few weeks.
When police arrived at that home Friday, they found a floor slick with blood and a man — Roberts' boyfriend — trying to revive a lifeless baby boy.
Emergency workers took Roberts and the child to the hospital. Doctors weren't able to save the baby, and they could tell that Roberts hadn't given birth. Although police aren't saying whether she really is pregnant, Washington County District Attorney Bob Herman said investigators are working under the presumption that she is not.
Police went back to Roberts' home and found Snively's body.
The story is not the first of its kind. About this time last year, a Pennsylvania woman was charged with murder after she cut a baby from another's woman's body and tried to pass it off as her own. The mother died.
In 2004, a Missouri woman strangled another woman with a rope and then used a kitchen knife to cut a baby girl from her womb. She was arrested one day later after showing the child off as her own.
In the Oregon case, a medical examiner said Snively had died of homicidal violence: "blunt force" causing head wounds and "sharp force" injuries to her stomach.
Authorities haven't offered a motive as to why Roberts, who has two children under the age of 10, might try to steal a baby in such a way or why she chose Snively's.
Investigators were also awaiting details from the autopsy and other tests to determine whether the baby might have breathed even once before he died. If he did, Roberts can also be charged in his killing.
Prosecutors will present their case to a grand jury for possible additional charges, Herman said. Roberts' boyfriend is cooperating and doesn't face charges.
A modest memorial for Snively and her son sat outside Roberts' home. At the center, amid bunches of flowers and stuffed teddy bears, was a handwritten note: "May God be with you."
Neighbors, the few who knew Roberts, weren't sure what to make of the allegations.
"You get the impression that whoever did this must be crazy," said next-door neighbor Terry King, 61. "But this woman didn't seem crazy on the surface."
Roberts smiled and waved whenever King saw her. She had told his wife she was expecting soon.
Snively's friends and family are just as confused.
"Knowing her and seeing her just a few weeks ago ... I just think about her last minutes," said Carson, the Maryland neighbor. "That baby was ready to be born."
One day before the slaying, Carson's daughter got a note from Snively. She loved Oregon and couldn't wait to meet her child.
"John Stephen," Snively wrote, "will be here soon."