Surveillance footage of a family of four walking over the U.S.-border and into Mexico fits the description of the San Diego family who have been missing for more than a month, according to authorities.
The video was shot at the San Ysidro Port of Entry on Feb. 8, just four days after the McStay family was last heard from, San Diego Sgt. Roy Frank told ABC News' affiliate KGTV.
Frank said that the family spotted on the video seemed to be "casually strolling into Mexico" and that each adult was holding hands with one of the toddlers. There was no sign any of the family members were in distress.
Joseph McStay, 40, and his wife, Summer, 43, disappeared along with their two children, Gianna, 4, and Joseph, 3, from their their serene San Diego-area community more than a month ago.
Even without a positive identification that the family in the video is the McStay family, investigators are pleased with the new information that they are characterizing as a "lead" in the mysterious case.
"What we see in this video is a lead and that lead is encouraging to us," Frank told AOL News. "We can't be sure that it is the McStay family, but we do know their vehicle was parked about five minutes away, walking distance, on the same day the video shows a family of four walking across the border."
The McStay's car, a white 1996 Isuzu Trooper, was found with the children's carseats still intact nearly 80 miles from the family's home, raising questions about any possible ties the family may have to Mexico.
But Joseph McStay's brother, Mike McStay, doubts that the family on the surveillance tape is his missing relatives.
Reached by phone, McStay declined to comment, instead referring ABCNews.com to the blog he set up to aid in the search of his brother, sister-in-law and two nephews.
Writing that he has seen the videos, McStay says he cannot be sure that it is his family.
"The video quality is very poor, I personally could NOT make a positive identification," he wrote.
"Careful reviews of the video shows that there are two or three different families passing by, one with a little girl actually, and the other with a man who walks nothing like my brother," wrote McStay.
Family Members Disagree Over McStay's Ties in Mexico
McStay and his father, Patrick McStay have disagreed since the family went missing in early February as to whether Joseph McStay might have any reason to travel to Tijuana, the Mexican border town closest the Southern California.
Joseph McStay is the owner of Earth Inspired Products, a company that designs interior decorative fountains, according to its Web site.
His brother said the fountain business shipped worldwide regularly, but he was unsure whether the two young children even had passports.
Their father, Patrick McStay, said he believes his son had done business in Tijuana, possibly as recently as December.
"I know he does business periodically," said Patrick McStay. "Some of the smaller fountains he offers are manufactured in Mexico, so he calls down there and has them sent to him."
McStay said he knew a lot about his son's business because he was the initial investor in the company. He also said he knew his son had been to Mexico, or at least to the nearby border towns, late last year to pick up granite countertops for his home kitchen, which he was renovating.
A San Diego Sheriff's Office spokeswoman said the U.S. Border Patrol and Interpol, the International Criminal Police Organization, are aiding the investigation, which includes homicide detectives.
"It did not appear that this family was planning on going on a vacation, and the dogs were not being cared for," Lt. Dennis Brugos of the San Diego Sheriff's Office said in a previous interview.
"We've been strategizing to figure out where they might be," Brugos said. "We're working with border control to find out whether there is any activity on their passports, and whether they had any connection to narcotics or gangs, but it doesn't seem as though they do."
"It's an absolute mystery," he said.