A member of the family of 12 believed to have travelled to Syria was stopped by police and their home was searched the day before they left the UK, it has been revealed.
One of the group - thought to be 21-year-old Rajia Khanom - was spoken while they were at Heathrow Airport on April 9.
She was not arrested but at the same time the family's home in Luton was searched.
Police insisted that there was no indication then that any of them planned to go to Syria and they were allowed to travel unimpeded the next day.
An investigation was launched when the group - including three children and two grandparents with health problems - failed to return from a holiday in Bangladesh.
They have reportedly made contact with relatives in the UK to state that they are in Syria.
Muhammed Abdul Mannan, 75, and his wife Minera Khatun, 53, are missing, with their daughter Ms Khanom, and sons Mohammed Zayd Hussain, 25, Mohammed Toufique Hussain, 19, Mohammed Abil Kashem Saker, 31, and Mohammed Saleh Hussain, 26.
Three unnamed children aged between one and 11 - a son of the older couple and two grandchildren - are with the group, as are Mohammed Abil Kashem Saker's wife Sheida Khanam, 27, and Mohammed Saleh Hussain's wife Roshanara Begum, 24.
Reports today claimed that Ms Khanom may have had links to banned Islamist group Al-Muhajiroun.
Her brother Mohammed Akhtar Hussain, who reported the family missing, told Channel 4 News his sister was initially prevented from flying when she was pulled aside at the airport.
"She didn't have any of her own luggage to check in because everyone's luggage was mixed in together," Mr Hussain told Channel 4 News.
"But the officers thought this was odd as she was supposed to just be going on holiday."
He is adamant his father would not have wanted to go to a war zone.
"I've been worried sick about my father, he's not in the best of health," he said.
The party initially travelled to Bangladesh from Heathrow via Istanbul on April 10, before flying back to the Turkish city on May 11.
They were due to come back to London three days later but failed to return and were reported missing by a relative on May 17.
Bedfordshire Police today confirmed that one of the members of the party was stopped at Heathrow Airport and subjected to an examination under Schedule 7 of the Terrorism Act 2000 on April 9. The force did not identify which individual was stopped.
A spokesman said: "At the time the Schedule 7 was taking place, a search was carried out at their home address in Spencer Road, Luton.
"There was no information, either through the Schedule 7 or search, which suggested that any of the family were intending to travel to Syria, so they were allowed to travel the following day without any police intervention.
"While the suggestion is that the party's current location is in Syria, this remains uncorroborated and our inquiries are continuing."
Meanwhile, a woman claiming to be a relative of the group said they are "just a normal, standard, average" family.
"You have a laugh, you have a giggle, you have fights, it's everything is normal as you would expect with any family household," the woman, who gave her name as Salma, told LBC's Ian Collins.
"So all of a sudden for them to just literally pack their bag and go and then they go missing and they don't come home.
"That's when you know you start putting everything together and thinking how, where, why, what? What triggered it? Everything was normal. There was no signs. There was nothing."
Asked what had led to this scenario, she said: "We have no idea because as, I reckon, you know, some way, somehow, you know there's been a lot of brainwashing going on."
She said the group were in touch when they were in Bangladesh. "They were having lots of fun, lots of family photos," she said.
"There was nothing in there to...to take that something was wrong."
Bedfordshire Police and Crime Commissioner Olly Martins said police were in "a very fraught and difficult area" when dealing with individuals that might travel to Syria.
He told BBC Radio 4's World at One: "As we've seen, they may have grounds for stopping someone but ultimately they were allowed to travel and events have developed in the way that we've seen."