April 29, 2012 -- A man captured in a surveillance video could be a key witness in the case of a missing Tucson, Ariz. girl as authorities expand their search into Mexico.
A group of five people were captured on surveillance video leaving a club near the Celis family home around the time the 6-year-old disappeared.
The three women and two men were captured on camera just a block from the Celis house.
Police said the group was walking away from a club at 1:30 a.m. in the direction of the Celis' home.
One of the men has come forward to police, but police are not yet saying what he has told them.
The new surveillance video comes as the search for Isabel widens, crossing over into Mexico.
On Saturday, U.S. marshals asked Mexican police for help checking hotels, bus terminals, and businesses in the Mexican border state of Sonora where Isabel's photo is being circulated.
"The idea of having Mexico involved I think is a logical idea and a good idea at this point…"The idea that somebody crossed and picked up Isabel and then went back into Mexico is actually realistic," said former FBI agent and ABC News consultant Brad Garrett.
Tucson is close to the Mexican border and many in the city are either from Mexico or have connections there.
Isabel Celis was reported missing by her father around 8 a.m. April 21 after her mother left for work and her father went to wake her up. The child was not in her room, and a bedroom window was opened with the screen removed, police said.
She was last seen around 11 p.m. April 20, when she was put to bed.
"If this child were abducted out of her house, through a window, out a door, somebody may have seen that," said Brad Garrett, a former FBI agent and ABC News consultant.
While the police have not ruled out Celis's parents as suspects, they have said the family has cooperated fully with police during the investigation.
"We have tremendous gratitude to the millions of people around the world who have prayed for Isabel," Becky Celis said. "Please continue to pray for her return. We don't want the focus to be taken off Isabel by talking in front of the cameras."
A dog from an FBI search team that included a scent dog and a cadaver dog hit on something in the house that police noted was "important" to the investigation on April 22. Police then executed search warrants on the Celis home and other homes in the neighborhood, though they would not say which ones.
Authorities are awaiting lab results of the evidence gathered, sources told ABC News.
Police have searched homes in the family's neighborhood, dug through a nearby landfull and searched waterways and drainage systems in Tucson, but so far have few leads.
The missing girl's parents issued a plea this week for the safe return of their daughter.
"Just please, please, to the person or persons who have Isabel, tell us what you want. We will do anything for her. We're looking for you, Isa," Sergio Celis, the girl's father, said tearfully.
Standing with family members clad in matching "Bring Isa Home" T-shirts, Celis and his wife, Becky,spoke directly to their daughter's captor, saying in both English and Spanish that they would do anything for her return. The parents have offered $6,000 for information about her disappearance.
Police noted that there are 15 registered sex offenders in the neighborhood, all of whom have been interviewed by police.