He met her for the first time on the night she died.
Appearing at St Albans Crown Court, Judge Andrew Bright QC said he will sentence Carl Langdell on Friday.
Prosecutor Ann Evans said: "The tragedy of this case is that Katie Locke, like thousands of other young people, having agreed to a date with Carl Langdell accepted what he told her about himself.
Read more: Tory MPs demand David Cameron probes claim EU referendum polling cards were sent to foreigners "At the end of their first date in the early hours of 24 December last year she agreed to go back to a hotel with him, he strangled her in that hotel room and then dumped her body near a skip outside the hotel." Katie, who graduated from Southampton University, was described as "beautiful and vibrant" by her family.
A sick and twisted fantasist violently assaulted and strangled a young teacher he met on the Plenty of Fish dating site before having sex with her dead body, a court has heard.
Carl Langdell met Katie Locke on the dating app Plenty of Fish.
When they met up, he took her back to the four star Theobalds Park Hotel in Hertfordshire where he violently attacked and killed her.
St Albans Crown Court heard how he dumped her body in a bush near a skip in the 55-acres grounds after strangling her to death.
He then took photos of the 23-year-old's dead body, and sexually assaulted her.
He also admitted that he wanted to see her naked and have sex with her when she was dead.
Read more: Teenage girl with mental health problems died after Priory staff neglected her Katie had taught history and politics at Cardinal Pole School in Hackney, east London.
Before they met, Langdell lied to Katie when he said he had his own law firm.