For Francia De La Rosa, nothing is more painful than the passage of time.

It's been more than three weeks since her pregnant daughter, Linoshka Torres, and Ms. Torres' boyfriend, Luis Campos, disappeared in broad daylight from a driveway at a home in central Oak Cliff.

"Nobody can know how we feel," Ms. De La Rosa said. "[When] I see something like that on the news, it hurts. But when it's yourself, it's worse. Really, nobody can imagine."

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Relatives insist Linoshka Torres and Luis Campos have no enemies who would want to harm them.

The mystery of the young couple's disappearance baffles their families and police.

Nothing seems logical about the way Ms. Torres, 18, and Mr. Campos, 20, went missing. Neither had criminal records, and there was no sign of foul play – just the red Ford Explorer they'd arrived in.

"The mystery part is we don't understand why this couple would disappear," Dallas police Sgt. Richard Wilson said. "They don't have anything that is of any value to anyone, and we don't see them as what you would consider an obvious target of someone that harm is going to come to."

The last time relatives heard from them was Jan. 6. Ms. Torres spoke on the phone with her mother, just like she did every day.

"I asked if she wanted to come over here to dinner and I'd cook for her," Ms. De La Rosa said. "She was going to come over."

Ms. De La Rosa prepared a meal of ham, potato salad and rice to celebrate Three Kings Day, a Catholic holiday that honors the three wise men who followed the Star of Bethlehem to take gifts to the baby Jesus.

Before dinner, Mr. Campos and Ms. Torres drove his father's Explorer to the home of Francisco Iniguez, a mechanic who does work at his small brick home in the 3300 block of Edgefield Avenue. Mr. Campos was going to pick up his 1998 Mustang, which had transmission problems.

Mr. Iniguez did not respond to several interview requests, but he has previously told WFAA-TV (Channel 8) that the couple were going to come by to get the car earlier in the day. When they didn't show up, he left.

Then the mechanic's son, who was looking through a window, saw the couple sitting in the Explorer sometime around 4:30 p.m., police said.

The mechanic's son declined to comment through a family friend.

Moments later, police said, the son looked back out the window and saw what may have been an older-model gray or tan Chevrolet Lumina with tinted windows that had pulled up behind the Explorer.

"It was suspicious to him," Sgt. Wilson said.

What happened next is unclear.

"He's not positive they jumped into that vehicle or went into that vehicle," Sgt. Wilson said. "It drove away at a fairly normal pace, so there wasn't anything suspicious other than the totality of the circumstances."

The couple had vanished, leaving behind their cellphones and keys in the ignition.

"That was so weird," said Pass Campos, Mr. Campos' sister-in-law. "She never left her cellphone. When she goes to sleep, she always put it under her pillow. She never leaves her phone."

Mr. Iniguez told WFAA that he was concerned about Ms. Torres and Mr. Campos, who came by almost every day to check on his car and chat. Mr. Iniguez said he was helping the young couple get a baby crib, and the Iniguez family had recently given the couple a new dress for their expected daughter.

Police said they have interviewed Mr. Iniguez and his son several times.

"We've had conversations with them, and we've been satisfied with the answers that have been given," Sgt. Wilson said two weeks ago. "The people that are involved that we've talked to don't have any red flags that pop up on them."

On Tuesday, Sgt. Gary Kirkpatrick, head of the department's Special Investigations Unit, said nothing has been ruled out.

"Even though we've talked to them originally and they appeared to be cooperative, we are double-checking all the information at this point in the investigation to make sure everything we were told in the beginning was true," he said.

Relatives insist Mr. Campos and Ms. Torres have no enemies who would want to harm them and gave no indication they would want to harm each other.

The pair met at a mutual friend's party last year. Ms. Torres, an honor roll student at Wilmer-Hutchins and South Oak Cliff high schools, quickly fell in love with Mr. Campos, a warehouse stocker and standout soccer player.

In the nine or 10 months they dated, the two became like Velcro.

"To us, she's the baby of the house, so we thought it was puppy love," said Rachell Torres, Ms. Torres' sister. "You see now it's serious. She was pregnant."

The family learned in August that Ms. Torres was expecting.

"We were amazed she wasn't depressed. We're a strict family," said Ms. Torres' other sister, Michelle. "We still live with my mom and stepdad.

"At the beginning, they were kind of upset, but they thought she will have to grow up and take responsibility."

Though the pregnancy seemed to come as a surprise, Ms. Campos said her brother-in-law was committed to starting a new life with Ms. Torres and their child.

"I think they were going to get married probably in January or February," she said.

The couple had recently signed a six-month lease on an apartment at the Dallas-Duncanville border, where they lived with their gerbil and hamster.

Their apartment manager was one of the last people to see them.

"The first time I saw them was the day they went missing," said the manager, who declined to give her name. She noted that Ms. Torres was visibly pregnant and that the couple seemed happy. "Everything was OK. They didn't seem like they'd be in any harm."

During their brief conversation, Mr. Campos asked her how much he owed for rent and a late fee. He handed over $489, and the couple left.

A few days after their disappearance, Rachell Torres came by to pick up their pets.

The couple's relatives oscillate between talking about them in the present and past tenses, as if they're torn between staying optimistic and resigning to dwindling hope.

Rachell Torres said she thinks police didn't take the case seriously enough in the beginning.

"The first couple of days they didn't do anything because they said they were old enough" to go off on their own, she said. "They said they were probably at a club."

Dallas police Sgt. Reginald Matthew, supervisor of the missing persons unit, said the missing persons case was elevated to "critical missing" within a day of the report, which means at least one patrol officer each shift continues searching for clues.

Four days after the couple were reported missing, the case was assigned to the department's Special Investigations Unit. Dallas police Assistant Chief Ron Waldrop said he made the move the same day he was briefed.

"We're concerned there may have been foul play," Chief Waldrop said. "We've thrown all the resources we can to try to figure out what happened."

Police have examined cellphone records and have been trying to locate people the couple talked to recently, Sgt. Wilson said.

"I feel like we're getting closer each day, but we can't name any suspects at this point," Sgt. Kirkpatrick said.

He said police are considering whether the couple may have been the victims of mistaken identity.

"It's a possible scenario," Sgt. Kirkpatrick said. "Since the location that they were last seen at was several miles from their house, we do see it as a possibility, but we're not ready to say it's an absolute certainty."

Mr. Campos is from Puebla, Mexico, but has lived in Texas for years. Police and family do not believe the couple decided to cross the border. Nevertheless, they've notified law enforcement authorities along the border to be on the lookout for them.

Schepps Dairy has announced a $10,000 reward for their safe return. If foul play is involved, the same reward is available for information leading to the arrest and indictment of those responsible.

"We're just waiting for a call," Ms. Campos said. "If they want money, we'll figure out how to get it."

The couple's baby is due in April.

"We want to see them again alive," said Leonor Alberto Campos, Mr. Campos' father. "My biggest fear is for someone to mistreat them or find them dead."