It's been 12 days since Michigan mom Tara Lynn Grant was last seen, and police have few clues as to her whereabouts.

The 34-year-old woman's husband said she walked down her dimly light driveway in Washington Township, got into a dark sedan and vanished.

Stephen Grant told police that his wife left home just hours after returning for the weekend from her job in the Caribbean on Feb. 9, police confirmed to FOXNews.com. The couple had a disagreement that night about the amount of time Tara spent away from home, her husband and her two children, ages 4 and 6, Macomb County Sheriff Mark Hackel told FOXNews.com

Grant commuted weekly to her job as acting general manager at Washington Group International's San Juan facility. The company is an international construction contractor. She had been traveling there every week since the beginning of the year; before that, she would commute about once a week every month, for about six months, according to her sister, Alicia Standerfer of Ohio.

She left the house about 11:15 p.m. Feb. 9, Stephen Grant told authorities, got into a black sedan waiting and disappeared. Tara — described as 5 foot 6, 120 pounds, with brown hair and eyes — never boarded her flight from Detroit to Puerto Rico on Feb. 11, authorities said.

Neither her cell phone nor her credit cards have been used since. Police said no one in the neighborhood say they saw any sort of black car in the Grants' driveway that night, and no area car service companies sent a vehicle to their house, either.

"It's very suspect — there are still a lot of questions still unanswered," Hackel said. "No one has seen or heard from her since her husband last saw her ... Nobody's seems to know where she's at."

Grant flew from Puerto Rico on Feb. 9, to Newark, N.J., then on to Detroit. She spoke to Standerfer twice that day — once around 11 a.m. while she was still in Puerto Rico, and again around dinner time when she was at the Newark airport.

After arriving in Detroit, Grant got her car out of the paid parking lot then drove home. She and her husband had a disagreement later that night, she packed a bag, then left, Hackel said. There is nothing in her cell-phone records to indicate she called anyone to come pick her up that night, he added. Her car was still in the garage after she went missing.

Authorities have checked area hospitals, and have been in contact with authorities in Puerto Rico in their search for Grant — all to no avail, Hackel said. No one in her office down there has heard from her either.

"This is extremely unusual for her to not be in contact with people at work either. … She had a very well paying job and really liked her work," Hackel said.

Members of Grant's family have descended upon the Detroit area to help in the investigation and to keep the case at the forefront of peoples' minds.

Standerfer, and some other relatives spent the weekend putting up fliers in the area and canvassing nearby neighborhoods looking for information on her whereabouts. They met with the detective handling the case on Sunday. Standerfer also spent time with her sister's children and husband.

Grant's 4-year-old son "may be aware that Mom's gone ... but he's not really aware of anything other than that," Standerfer told FOXNews.com. She said her 6-year-old niece, on the other hand, is "very intuitive, very smart for her age. She definitely knows that there's something going on but she doesn't know exactly what."

Standerfer said there were obvious stresses in her sister's life with the commute and her job and how that affected her family, but there was nothing that stuck out to her as out of the ordinary.

"I can tell you — obviously every scenario has gone around in my head about what could've happened," Standerfer told FOXNews.com. "Could these stresses have made her want to leave and disappear? Yes, absolutely. ... Do I think Tara was there? I don't think so necessarily ... I don't think things were that bad that she would just up and leave."

Standerfer said there was no one extremely close friend of her sister's with whom she may have shared any internal strife.

"We talked, we kept contact with each other as sisters, but as far as my sister's opening up about personal things ... she just didn't and I respected that," Standerfer said, adding that aside from some close coworkers, "as far as that one girlfriend that would know everything, no, she didn't have that one friend."

Sheriff: 'Nothing is Ruled Out'

Stephen Grant, who cared for the children and also had a full-time job with his family business, reported his wife missing on Valentine's Day.

When asked why Stephen Grant waited to contact authorities, his lawyer David Griem told the Free Press, "he believed that the reason she wasn't calling was because of the words they had."

Hackell told FOXNews.com that Stephen Grant could still be considered a suspect: "Nothing is ruled out right now — this is still all up in the air."

Police asked Stephen Grant initial questions about his wife's disappearance the night he came to the police station to report her missing, Hackell said, and when they returned to his house later that night.

But the relationship between Stephen Grant husband and police apparently became strained after he was arrested on Friday, Feb. 16, for speeding and having a suspended license. He claims that he was held for several hours in custody and interrogated about his wife's disappearance.

"I thought this is something that went out with the '50s," Griem told the Detroit Free Press. "What it's called is a pretext arrest: Arresting a person for one purpose but really it's for another."

But the sheriff's office denies any sort of interrogation took place, and that the officer who arrested him had no idea about his wife's investigation when he was initially pulled over. Hackel said he was brought to the booking desk and released about four hours later. Hackel stressed that police never said he was a suspect, but that Stephen Grant may have made himself one by going on television and mentioning that authorities always look to the husband in cases such as this.

"Whether people are going to be suspect or suspicious of him is going to depend on him and how he reacts," Hackel told FOXNews.com.

When asked if she thinks her brother-in-law had anything to do with her sister's disappearance, Standerfer said: "I'm not going to answer that directly. Obviously I feel comfortable enough with the family. I went to his house, I went out to dinner with him. … I spent extensive time with him and his kids."

She added: "Our communication lines amongst our family are open. They have never been shut down and they will remain open."

Hackel said he offered for Stephen Grant to take a polygraph test the night he reported his wife missing, and he agreed. But on Thursday, his lawyer said no. Now, Hackel said, police can't even talk directly to Stephen Grant, but have to ask him questions via fax through his lawyer.

"We don't care about the polygraph. Just give us information and help us here try to find your wife," Hackel said, adding that police want to access the Grants' computer at their house to see if there are any clues there. "He will be very instrument in trying to locate her and find her. His willingness is going to be very important in this case."

"We haven't exhausted all of our leads … there's a lot of other inquiries we have" of the husband, Hackell added. "Our concern is trying to find Tara and reunite her with family or at least get an idea of where she's at."

Anyone with information about Tara Lynn Grant's whereabouts is asked to call the Macomb County Sheriff's Office at (586) 307-9358, or after hours (586) 307-9412.