A man has been found guilty of murdering a transgender woman after a sex and drugs binge.

Jesse McDonald, 25, contacted 36-year-old Naomi Hersi through the dating website Fabswingers, the Old Bailey heard.

Naomi Hersi. Photograph: Twitter

After a three-day sexual encounter, McDonald drugged Hersi then stabbed her to death with a knife and a broken bottle at a hotel near Heathrow airport where he was living.

He then lied about it as he recruited his 18-year-old girlfriend, Natalia Darkowska, to help clean up, jurors were told.

Mark Heywood QC, prosecuting, said McDonald had planned to dispose of the body but the victim was found half-naked, partly covered by a rug on the bathroom floor.

McDonald admitted causing the fatal injuries but denied murder, claiming he acted in self-defence. He and Darkowska, from Trowbridge in Wiltshire, both denied perverting the course of justice. A jury deliberated for 17 hours to find them guilty of the charges.

The pair cried in the dock and McDonald bent over with his head in his hands before hugging his girlfriend, saying: “I’m sorry.”

The court heard that Hersi, whose legal name was Hersi Mohamed Hersi, was an openly transgender woman.

McDonald, who grew up in West Sussex, was said to have done well in school and played tennis at county level but began dealing drugs and trading in bitcoin after dropping out of the London School of Economics.

On 12 March, he contacted Hersi within 45 minutes of returning to the hotel in Hounslow from visiting his girlfriend.

He drove his BMW to the victim’s home in Mill Hill, north-west London, where he stayed for three days before they went back to his hotel room.

Throughout that time, McDonald is said to have ignored his girlfriend’s increasingly frequent attempts to contact him. But on Friday 16 March he sent her a message which said: “Baby I been a f****** idiot.”

Another read: “I love u so much. Not cheated x. Got addicted to a nasty drug I had never met before.”

He then told her he had “got a big drug dealer” lying across his floor, adding “won’t wake up ... massive black guy”.

While the defendants were cleaning up, McDonald phoned his mother and claimed he had been chained up for days, drugged and repeatedly raped. McDonald alleged he had stabbed Hersi up to 40 times in a frenzy, believing she was about to smother him with a pillow.

His mother, from Haywards Heath, phoned the police. The defendant also offered his landlord a designer watch if he cleared up his room before confessing he had killed someone, jurors heard.

About 10 minutes after his last call, police arrived at the property and found Hersi’s body and the murder weapon. The defendants were tracked down to a hotel in Teddington and arrested.

During his police interview, McDonald continued to claim he had been bound and raped. Giving evidence, the Brighton-born defendant said he had contacted Hersi online “because I’m a complete idiot”.

He said: “Clearly I was looking for something, I wanted to get out. I don’t know, it is not uncommon for me to have done something like this in the past. I’m disappointed in myself.

“At the time I felt open-minded, liberal-minded, whatever you want to call it.”

Following his conviction, Det Insp Tom Dahri, from Scotland Yard, said: “From day one of this murder, McDonald has spun lie after lie and tarnished the name of the victim by calling her some of the vilest names in front of her family.

“McDonald completely fabricated that he was kept against his will at Naomi’s address and there was no evidence whatsoever that he had been raped by her, either.

“This was all just smoke and mirrors to make himself look like a victim, when in fact he is a cold and calculated killer who dragged his girlfriend in to help him clear up his mess. We are very pleased the jury saw through his tissue of lies.

“Naomi Hersi was a transgender woman, and will be much missed by all those who knew her, especially by her family.”

He thanked the police’s partners in the LGBT communities for their support and advice during the investigation.

Angela Moriarty, from the Crown Prosecution Service, said: “This encounter between two strangers, who had consumed a quantity of drugs, led to the tragic death of Naomi Hersi.

“McDonald claimed he inflicted the fatal stab wounds in self-defence but the prosecution was able to prove to the jury that this was not the case, and McDonald had willingly spent days with the victim – even going shopping to Sainsbury’s and Tesco stores together.”

“The defendant also confessed to the murder while on the phone to the owner of the hotel, telling him he would give him his designer Porsche watch if he cleaned up the bloodied room.”

McDonald was remanded in custody to be sentenced next Friday. Darkowska, who was granted continued bail, will be sentenced on 16 November to allow time for a probation report to be compiled.