LONDON — The son of Dawn Sturgess, a British woman fatally poisoned by a nerve agent discarded in a residential area by Russian intelligence officers, on Sunday asked President Vladimir V. Putin to allow British investigators to question the men presumed responsible, telling Mr. Putin, “I am appealing to you as a human being.”
“Allow our officers to question these men about my mother’s murder,” he urged Mr. Putin on the anniversary of the nerve agent attack, according to excerpts from a letter published in The Mirror. “The least she deserves is justice.”
Ms. Sturgess, 44, and her boyfriend, Charlie Rowley, 45, were collateral damage in the attack on Sergei V. Skripal, a former Russian spy who had been resettled in Salisbury, a quiet city in southern England. Since Ms. Sturgess’s death, Russian officials have repeatedly made light of the incident. In December, the state-run television network RT sent chocolate replicas of Salisbury Cathedral as holiday gifts.
On Sunday, Ms. Sturgess’s 20-year-old son, Ewan Hope, addressed Mr. Putin directly.
“He needs to show he’s capable of showing some humanity to our family,” he said. “I would ask him to imagine how he would feel if he was in my shoes.”
Ms. Sturgess and Mr. Rowley, who survived the poisoning, had struggled with addiction, and when they fell ill on July 1 — nearly four months after the attack on the Skripals — the police initially suspected an overdose or a contaminated batch of drugs.
But their symptoms — foaming at the mouth, pinpoint pupils and hallucinations — were similar to those that had emerged with the three previous victims: Mr. Skripal, his daughter, Yulia, and a detective who was exposed while responding to the crime.
Mr. Hope described his frustration at watching the two Russian intelligence officers presumed responsible, Anatoly V. Chepiga and Aleksandr Y. Mishkin, give a poker-faced interview to RT. They claimed they were sports nutritionists who had visited Salisbury because they had heard of its remarkable cathedral.
“I was so angry,” he told The Mirror. “They looked so smug and happy with themselves. But I felt a sense of relief as well because I thought something would happen and that they would be caught. Now I feel like we’ve been lied to.”
Mr. Hope continued, “The strange thing now is we know who killed Mum, the evidence is there and we know how it happened, but we can’t get them to face justice.” In the absence of a trial, he said, “it’s going to upset me for the rest of my life.”
At the time of the poisoning, Ms. Sturgess was living in a state-run shelter that houses people with drug and alcohol problems. Other residents spoke fondly of her, describing her as a maternal figure who propped her door open with a sock so that her friends could stop in to see her at any time.
She had been buoyed by her relationship with Mr. Rowley, who was recovering from a heroin addiction.
“I trust Charlie with my life and he gets me the best gifts ever,” she wrote on Facebook.
It was one of those gifts, a vial with a counterfeit label identifying it as Nina Ricci perfume, that killed her.
Ms. Sturgess is believed to have sprayed the substance on the inside of her wrist on July 1. A friend who was with Ms. Sturgess and Mr. Rowley said that their condition rapidly deteriorated. Ms. Sturgess lived for a week after her exposure.
Her family said little at the time, but expressed anger as the anniversary of the poisoning approached.
Her mother, Caroline, recalled that she was allowed to touch her dying daughter only if she was wearing protective gloves. At one point, she said, she reached up to wipe away a tear and was warned by an official not to touch her own face.
Her son, Mr. Hope, also recalled touching her as she lay in the hospital.
“I touched her hair through the gloves and told her: ‘I love you, Mum. I just want you to get better,’” he told The Mirror before she died. “I’m worried I’m going to lose my mum.”