Arreguin, a lifelong East Palo Altan who was educated in Palo Alto schools from kindergarten through high school, died of multiple gunshot wounds to his upper torso in a 9:30 p.m. incident on Jasmine Way.
"We believe we have a motive, and we're just trying to put the pieces together and detain the right people and make a positive arrest," East Palo Alto Police Capt. Carl Estelle said Thursday morning.
"We're following up on more leads and are in the middle of some more interviews to try to determine who was responsible.
"I can't tell you the motive because it would tip our hand."
Estelle declined to comment on whether drugs or gang activities were involved in the murder.
A funeral mass was held Thursday morning for Arreguin.
"Gabriel was not involved in gangs or drugs," his godmother, Jennifer Espinoza of Palo Alto, said Tuesday.
"There were no witnesses, and no motive other than robbery," said Espinoza, who first met Gabriel's mother, Socorro Arreguin, more than 20 years ago through an outreach program from Peninsula Bible Church of Palo Alto.
A short time later Gabriel, the eighth of nine children, was born and Socorro Arreguin asked Espinoza to be the boy's godmother.
"She became my dear friend," said Espinoza, a longtime Palo Alto resident and retired Spectra Art teacher in the Palo Alto Unified School District.
"Gabriel is the last one I'd ever think would die this way," Espinoza said.
"He's so sweet, such a good friend, easy going, not a fighter — it's stunning."
Like all but one of his eight siblings, Gabriel participated in the Tinsley Voluntary Transfer Program, which allows 60 kindergartners from East Palo Alto's Ravenswood City School District to enroll in Palo Alto schools each year.
Gabriel went to El Carmelo Elementary School and Jordan Middle School. He attended Palo Alto High School but graduated from Alta Vista Continuation High School, an alternative program emphasizing personalized instruction, integrated study and vocational education and training.
"He went through some rough years in terms of typical teenage angst," Espinoza said.
"We went to his graduation. It was a very proud, happy day for everyone. It felt great to see him do that."
Socorro Arreguin worked for many years at Casa Olga in downtown Palo Alto until the residential facility closed last year.
Gabriel lived with his mother while working at PetSmart, from which he was recently laid off.
He helped by picking up nieces and nephews from St. Elizabeth Seton School in Palo Alto, where they attend.
"He was really devoted to his family. His sisters-in-law are saying how hard this is on the little ones.
The last time Espinoza saw her godson, in late April, she encouraged to find a job.
"He said, 'I will, I will.'"
"He was a huge animal lover his whole life," Espinoza said. "At different times he had dogs, chickens, a toad, lizards, pythons, parakeets, tropical birds."
Socorro Arreguin, who speaks limited English, has been surrounded by family and friends since her son's death, Espinoza said.
In a report issued last week, East Palo Alto police said were responding to calls that shots had been fired and were flagged down near the scene by a motorist who had put the bleeding Arreguin in the car's back seat.
Arreguin was transported to a hospital but died of his injuries.
Police ask witnesses to call Detective John Norden at 650-464-6822, or the department's anonymous tip line at 650-851-8477.
In addition to his mother, Gabriel is survived by his siblings Ramiro, Ismael, Fernando, Alejandro, Juan, Sandra, Jasmin and Jose; a grandmother in Mexico; many aunts, uncles, nieces and nephews. He had lost contact with his father.