Mr Justice Sweeney said the sentencing could go ahead in the absence of the defendant, Koci Selamaj, 36, as the court had no power to force him to attend.
The judge noted a life sentence was “inevitable” with a starting point for a minimum term of 30 years.
Selamaj, from Eastbourne, East Sussex, had admitted the murder of Ms Nessa at an earlier hearing.
Ms Nessa, 28, was attacked by Selamaj in a park in Kidbrooke, south London, on the evening of September 17 last year.
Prosecutor Alison Morgan QC said Selamaj had a history of violence against his former wife.
After leaving him, his wife told colleagues at the hotel where she worked that he had tried to strangle her.
Supporters from the Sabina Project outside the Old Bailey
Yui Mok
Supporters from the Sabina Project outside the Old Bailey
Yui Mok
Ms Morgan said she had been “devastated” by what Selamaj had done to Ms Nessa and commended her courage in coming forward.
The court heard how Selamaj had booked a room at The Grand Hotel in Eastbourne for Friday September 17 last year.
Alison Morgan QC suggested booking a room at the hotel near his home was “indicative of his premeditation to have some kind of sexual encounter that evening”.
At about 6pm that day, Selamaj contacted his estranged partner.
In a statement, she said he appeared “very agitated” when they met at his car near the hotel.
She said: “I think that he wanted to have sex in the car. I don’t know what was bothering him, but he was very agitated.”
She refused to join him on the back seat and left, the court was told.
Ms Nessa left her home at 8.32pm to meet a friend for a drink.
Mr Justice Sweeney adjourned the sentencing until 10am on Friday.
