Married David Hodgson, 47, then disposed of her body and started sending fake messages on her mobile phone to make it seem she was still alive, Teesside Crown Court was told.

Shop assistant Jenny Nicholl, then 19, has not been seen since she left her home in Bolton Avenue, Richmond, on June 30, 2005, telling her mother Ann she was staying out for the night.

Yesterday Hodgson, the father of two of Jenny's former schoolmates, denied murder.

The court was told that, on July 8, 2005, when Jenny's disappearance was still being treated as a missing person case, Hodgson was interviewed as a witness.

The following day Jenny's mobile phone – which had been silent since she went missing – was turned back on and text messages supposedly from Jenny were sent to friends suggesting she was still alive.

One read: "Everyone's going to be mad. Tell them I'm sorry. Living in Scotland with my boyfriend. Dad's going to kill me. Tell him I'm sorry."

The source of transmission was traced to a phone mast in Cumbria. Then, five days later, the phone was switched on again and a text transmitted from Jedburgh in the Scottish Borders to Jenny's father Brian.

James Goss QC, prosecuting, said: "These pairs of text messages are crucial. If they were genuine messages from her then Jenny was alive and well.

"Conversely if they were not genuinely from Jenny they were sent by someone who had possession of Jenny's phone...and by someone who had decided to send false messages purporting to indicate Jenny was still alive."

Mr Goss told the jury that expert analysis of the style of the messages suggested they were not sent by Jenny at all – but there were similarities with the way Hodgson composed his own texts, and he knew enough about her background to fake them.

Later that month Hodgson was arrested on suspicion of perverting the course of justice and he then became a murder suspect.

Mr Goss said Hodgson, unemployed of Olav Road, Richmond, formed a relationship with Jenny while she was studying at St Francis Xavier School where his own two daughters were pupils.

He allegedly formed a relationship with her when she was 14 and later admitted having sex with her but not before she was 16.

Mr Goss suggested the couple had enjoyed an intense and secretive relationship which may have been threatened when Jenny became interested in Hodgson's brother Robert.

Jenny and Robert had been close in the month before her disappearance. She had been spending nights at his flat, including the one before she disappeared.

He said jealousy because of the blossoming relationship with Robert was one possible motive.

The jury was told that Hodgson, who often went camping with his brother, knew the countryside around Richmond well including its army ranges, old mines, and deep rock faults.

He had created a number of camouflaged hides at Sandbeck Plantation near Richmond, where DNA evidence was found indicating he had had sex there with Jenny.

The teenager's teddy bear, pyjama top and radio cassette player were also found hidden at the spot when a fresh search was carried out in 2006.

Mr Goss said there was no logical reason for Jenny to dispose of these items, let alone hide them.

"Rather, these items had been concealed there by someone because it is known by them that Jenny had no use for them and, like Jenny, they should not be found," he said.

Mr Goss said extensive checks had established no trace of Jenny. Money in her bank account had not been touched, she had left no note, she had not told work she was leaving, and had even booked tanning sessions and arranged to meet a friend in a pub just before her disappearance.

The trial, which is expected to last six weeks, continues.