Joe Yates arrested her Dutch neighbor after a report.
The sun can be revealed from the crying girl.
After Joe's parents called for information this week, she called.
Yesterday, news of the dramatic anonymous phone call surfaced as detectives had more time to ask 32-year-old Vincent Tabak.
The court ruled he could be detained until tonight.
Meanwhile, the attic of the Bristol house where he was arrested was searched yesterday.
Police received the woman's message hours after posting this week's emotional TV appeal recorded for Jo's parents David and Teresa's BBC1 Crimewatch show.
They begged anyone with news to come forward.
A source said: "The caller said that what David and Teresa said moved her to tears and she felt that she had to pass on what she knew.
"The detective who opened up important new information about the investigation clues-year-The killer of old Joe.
David, 63, and Teresa, 58, read a statement saying they felt she had been murdered by someone she knew.
It is believed that this was specially drafted by the police with the help of psychological investigators, with the aim of piercing the conscience of anyone who concealed the information.
The couple warned: "If you know something and don't come forward, you will consciously block the arrest of Joe's murderer, who is still free.
"You will also extend the pain of Jo's family and friends.
They urge people to consider whether they have noticed that a close person is "out of character" or that he has become inexplicably "secluded, quiet or outspoken" since Jo went missing in December 17 ".
They asked: "Has anyone tried to leave you a scene that is inconsistent with the information that the police have posted?
"Do you know anyone defending her being killed?
Please help us find the killer.
"Joe's last known action appeal and reconstruction will be shown on Crimewatch next Wednesday.
The last time she was seen alive
Have Christmas drinks with colleagues
She was found strangled in an alley on Christmas Day.
Taebuck lives next to her ground floor apartment with her boyfriend Greg Ryden in the bristkirk livton area.
Two days after Joe went missing, 6ft 4 in beanpole went to the Netherlands to spend Christmas with his family.
On Thursday, he was arrested at an apartment on Aberdeen Road, about a mile from Clifton's house.
It is owned by 31-year-old accounting friend Emily Williams and her sister Lucy Williams, who is on vacation in South America.
Yesterday, forensics carried luggage from the property.
Tabak knows landscape architect Jo and, according to his former colleagues at consultant engineer Buro Happold, they work together to develop a joint plan for their respective companies.
They said: "They will meet at her office or place.
The source saw Tabak in the company's bathroom a few hours before Joe's disappearance and said: "He seems to be happy and happier than normally.
Others who used to live in the tabaklefton apartment said: "There can be no more hidden buildings.
No one can hear or see anything if you're walking around the back.
But I can see someone passing through my front window
The apartment is sunken so you can see Joe's legs but she doesn't know.
"You can move between his apartment and Jo's, or between the small parking lot next to it, no one will know.
"Another tenant who became a Tabak apartment said that he had never heard of the situation of being blocked --
Once connected to the doors of two apartments.
But he added: "There is only one thin partition wall.
Can you hear what happened next door?
Last night, the police and Tabak's girlfriend, we
Tanja Morson, 34, was born and lives with him.
Jeffrey, her Canadian lawyer and father of Cambridge, said rumors of her breaking up with Tabak after Joe went missing were "ridiculous ".
A neighbor who lives behind Joe's Apartment reportedly told police that the night she went missing, he heard a woman screaming "Help me ".
His story has to do with hearing reports of another neighbor crying. m. sullivan@the-sun. co.