Russian authorities continued Monday to question Anna Duritskaya, a 23-year-old Ukrainian model and girlfriend to slain Russian opposition leader Boris Nemtsov. Duritskaya was said to be the sole witness to Nemtsov’s murder Friday at the hands of an unidentified gunman.

Police said Duritskaya was being held for her own safety, according to the BBC. But Duritskaya has questioned her detention and expressed a desire to be temporarily released so that she can visit her mother, who lives in Kiev, Ukraine. “I don’t understand why I’m still on Russian territory,” Duritskaya told independent Russian news service TV Rain, according to the BBC.

Duritskaya and Nemtsov had dated for four years prior to his assassination, according to the New York Observer. The couple had “a very close personal romantic relationship,” according to Russian TV program Vesti.

Duritskaya is an actress and model who worked for modeling agencies before she began to date Nemstov. She also studied at Kiev University.

Nemtsov, a former deputy prime minister and an outspoken critic of Russian President Vladimir Putin, was shot dead on Moscow’s Great Moskvoretsky Bridge near the Kremlin as he and Duritskaya left dinner at a nearby restaurant, various outlets reported. The gunman exited a white vehicle and shot Nemtsov four times and left Duritskaya uninjured. Authorities have yet to identify the killer.

“I do not know who did it. I do not want to answer the questioned about the situation at the bridge, I do not want to talk about it,” Duritskaya said on TV Rain, according to the Daily Mail. “It is not forbidden for me, but my psychological condition is very hard now and I can’t talk any more about it.”

Duritskaya’s mother, Inna Duritskaya, said she spoke to her daughter on the phone moments before Nemtsov’s death. She also relayed her belief that Russian authorities were attempting to erroneously link her daughter to Nemtsov’s murder in order to implicate Ukraine, amid a monthslong struggle between pro-Russian separatist rebels and the Ukrainian government.

“I think they want to make her guilty, they want to set her up. What are their reasons to keep her? Everyone knows she had nothing to do with it,” Inna Duritskaya said. “I think my daughter is kept because this murder should be linked to Ukraine.”