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Maria Climaco, mother of Aya Nakano, the Emeryville, Calif. man who was shot dead following a minor traffic collision late on the evening of June 12, 2013, spruces up a memorial to her son at the spot on Market Street where he was killed, Thursday, June 12, 2014 in Oakland, Calif. (D. Ross Cameron/Bay Area News Group)

OAKLAND -- Aya Nakano always said, "My mom has my back."

A year after the 22-year-old Emeryville man's killing in North Oakland, Maria Climaco, Nakano's mother, is proving her son right.

She has put her life on hold to keep her only child's tragic story in the news, work with police, raise money to fund a sizable reward and remember the son she called her best friend.

"I owe it to Aya," she said Thursday, the anniversary of his murder.

Nakano was killed shortly before midnight on June 12, 2013, about an hour before his 23rd birthday. A dedicated Golden State Warriors fan who collected basketball shoes, he had graduated from the University of Oregon in 2012. He enjoyed dressing nicely, and his mother took pleasure in picking out and buying his work clothing.

"He calls me his stylist and his guru," said Nakano, who often slips into the present tense when discussing her son. "I ironed his outfits. I miss doing that for him."

Climaco is a tiny woman -- 5 feet tall and maybe 100 pounds -- and her dark hair is thinning from chemotherapy treatments she receives a few times a year for lupus, which struck her 17 years ago. Even with the fatigue she's faced since that diagnosis, the past year has been the most trying time of her life, she says.

"Hell does not begin to describe it. I have my good days, but mostly bad days," said the 47-year-old, who was married briefly to Nakano's father when the boy was small.

On the night he was killed, Nakano was returning to the family home in Emeryville for a late dinner after playing pickup basketball at the UC Berkeley recreation center. His Jeep Cherokee was rear-ended near a bus stop at Market Street and Stanford Avenue in North Oakland.

Nakano got out of his car -- presumably to exchange insurance information with the other driver -- and an argument ensued, police said. The unidentified driver shot him, and he and a passenger sped off south on Market Street in a late-model, four-door, silver sedan hatchback, police said.

That night changed Climaco forever. She and her partner of 17 years are now preparing to move to the Peninsula because they can't stand to hear the constant police, fire and ambulance sirens in nearby Oakland.

Climaco stays in regular contact with Oakland police Officer Eric Milina, the lead investigator on the case. She goes to the scene of the crime at least three times a week.

"I just park and talk to him," she said.

Her grief is palpable; she rarely smiles.

"A good day for me is enjoying memories of Aya. It's a double-edged sword, though. Those memories can also send me into a tailspin," she said.

She tries to hold back tears as she speaks, staring into the distance, clinching her teeth, looking at her hands. When she does cry, it seems to bring her a bit of relief, if only for a few seconds.

"Sometimes it hits me like a ton of bricks," she said.

When she speaks of his death, she says "the day it happened" or "the incident." She doesn't say "murder" or "killing."

"I can't," she said. "I just can't."

She said she sometimes wishes it were she who was killed that June night. Therapy has helped with the survivors' guilt, along with a large and supportive network of family and friends.

Finding justice for her son is what really keeps her going.

But she wants help.

Police want to talk to an unidentified woman who pulled up at the scene that night in another car but quickly left. Investigators received some tips but need more information from the community to solve the case, Oakland police spokeswoman Officer Johnna Watson said.

"We are asking for tips -- that small piece of information could be what solves this crime," Watson said. Anonymous tips are accepted, and a $100,000 reward is being offered for information leading to the arrest of the shooter. Anyone with information is asked to contact the Oakland police homicide unit at 510-238-3821.

In Oakland, where it's common to have more than 100 killings a year, the sizable reward raised by Climaco -- a mix of fundraising, private gifts, savings, a donation from the city of Emeryville and Crime Stoppers reward money -- is rare.

"It is unusual," Watson said. "It doesn't happen often."

Climaco is focused on keeping the story of Nakano's slaying "in the public consciousness." She has spent nearly$50,000 from her own savings to buy advertising space on 45 bus stop benches, five billboards and 15 AC Transit buses with a message about the crime, the reward and how to contact police. The ad campaign is set to end this month, and she is exploring ways to continue the effort.

On Thursday, the anniversary of the slaying, his mother went to the scene of the shooting and adorned it with flowers and teddy bears, along with signs to honor him.

"I'm not giving up," she said. "I have all the time in the world. However long it takes, I will keeping working on the case."

Follow Kristin J. Bender at Twitter.com/kjbender.