San Francisco Mayor London Breed has asked Gov. Jerry Brown to release her brother from prison, where he has served nearly two decades of a 44-year sentence for a manslaughter conviction in the death of a San Francisco woman, according to the mayor’s office.

Breed’s brother, Napoleon Brown, now 46, pushed 25-year-old Lenties White from a getaway car on the Golden Gate Bridge after an armed robbery in June 2000. She was struck by an oncoming drunken driver and died.

Breed sent a letter to Gov. Brown on Oct. 23 asking him to “consider leniency” and commute her brother’s prison sentence. The letter appears to have been sent on personal stationery, but the heading and the body of the letter reference her position as the city’s mayor.

The mayor’s letter was sent with similar messages of support from other family members, including Napoleon Brown’s mother, sister and cousin, as part of his application to have his sentence commuted, according to documents reviewed by The Chronicle.

The mayor’s letter to the governor was first reported Tuesday night by NBC Bay Area.

Napoleon Brown has served less than half of his 44-year-sentence for White’s death and the robbery of a Johnny Rockets restaurant on Chestnut Street in San Francisco.

Breed’s status as mayor could raise questions about whether the letter constitutes an improper attempt to use her status to influence the governor’s decision.

“I am very sorry for all the people I hurt with my crimes 18 years ago,” Napoleon Brown wrote in his letter to the governor, in which he details his efforts toward self-improvement while in prison. Though he blames his “crimes and bad behaviors” on addiction, he wrote, “I still take full and complete responsibility for all my actions.” And he asks for the opportunity to re-establish a relationship with his children.

In her letter to the governor, Breed said that “Napoleon struggled early on with a sense of hopelessness. And like many others, he developed a bad drug problem at an early age. His drug addiction led to a young life of crime.”

Breed has often portrayed her impoverished upbringing in Western Addition public housing as an example of overcoming obstacles to succeed in life, especially in a city with stark income disparities. In that narrative, she has mentioned that her sister died of a drug overdose and her brother was in prison.

Breed, 44, is two years younger than her brother. Her letter to the governor apparently contains the most information she has made public about his situation.

“Although I don’t believe the 44-year sentence was fair, I make no excuses for him,” Breed wrote. “His decisions, his actions, led him to the place he finds himself now. Still, I ask that you consider mercy, and rehabilitation.”

Documents contained in her brother’s commutation application indicate that his attorneys expected to negotiate with San Francisco prosecutors for a 20-year sentence, but the district attorney’s office would only consider a “package deal,” with both Napoleon Brown and his co-defendant, Sala Thorn, pleading guilty. Thorn wanted a trial, according to Brown’s commutation application.

Before she died from blunt force trauma and blood loss at a hospital, White told officers that Napoleon Brown had pushed her out of the getaway car she was driving, according to court documents filed in 2014 related to the case.

“Prison is not the place for him to stay clean, for him to make meaningful amends for his crimes, for him to pursue restorative justice,” Breed wrote in her letter.

The governor’s office did not immediately respond to requests for comment.

Court records filed in federal court detail the moments leading up to White’s death.

On June 19, 2000, Brown and Thorn, then 24, walked into the Johnny Rockets restaurant between midnight and 12:30 a.m. while employees were preparing to leave for the night. The two forced workers to lie facedown on the floor and pocketed more than $7,000 from a safe.

Police Officer Gary Watts told investigators that he saw both men “walking briskly” toward him on Chestnut Street soon after the robbery. One of the men was carrying a red bank deposit bag, and the pair turned the corner and ran to a white Ford Escort with its taillights on, Watts said.

White was behind the wheel. The men piled into the car on the passenger side and the car drove off.

Watts pursued the car after hearing a radio dispatch report that police were responding to a robbery at the restaurant. He asked the California Highway Patrol for assistance in stopping the vehicle, then sped ahead of the car and stopped at a parking lot near the bridge and waited for the Ford to pass him, according to the court documents.

After the Ford passed him and traveled onto the bridge, Watts followed closely behind but did not flash his patrol lights on the vehicle, he told investigators.

Soon after driving onto the bridge, the Ford pulled into the buffer lane in the middle of the bridge, the driver’s-side door opened, and White was pushed to the roadway, court records show. She lay sobbing facedown in the roadway, Watts said.

Watts told investigators that when he got out of his patrol car, he saw a man exit the passenger’s side of the Ford and walk toward the driver’s side. Watts said he told the man to lie on the ground, but he ignored the order, got back in the car and drove off.

Watts said he also yelled at White to get up, but she remained in the roadway and was struck by a Dodge Stratus. Its driver was arrested on suspicion of driving while intoxicated and vehicular manslaughter.

Before dying, White managed to identify Napoleon Brown as the man who pushed her from the car, calling him by his nickname of “S.B.,” and told police where he lived, police said.

Breed, who was 25 at the time, told investigators that when she arrived at her grandmother’s house around midnight on the morning of the robbery and White’s death, Brown was asleep on the couch, court records show. She said she could not remember if her brother was home when she left for work that morning.

Police Inspectors Anthony Camilleri and Antonio Casillas interviewed Breed the day after the robbery and she confirmed that her brother went by the nickname “Sonny” or “Sonny Boy,” according to court records. But the defense argued that Breed “denied ever telling the police that defendant used the nickname S.B.”

Napoleon Brown was convicted of manslaughter, robbery and other crimes. He was sentenced to 42 years, and received two years of extra time after prison officials found heroin in his possession while incarcerated.

He is currently at Solano State Prison.

Lauren Hernandez and Dominic Fracassa is a San Francisco Chronicle staff writer. Email: lauren.hernandez@sfchronicle.com, dfracassa@sfchronicle.com Twitter: @LaurenPorFavor