Organizers are frustrated that Gascon hasn't made a decision whether to charge the two officers involved. The organizers told the ABC7 I-Team they have little hope he will file charges, even though an autopsy concluded officers shot the man from behind.
In fact, the district attorney's office has never charged a San Francisco cop in an officer-involved shooting.
Amilcar Perez Lopez, 21, a carpenter and construction worker was allegedly shot to death by two plainclothes cops in the Mission District in February 2015.
Gascon says one of the main witnesses took a year to come forward and that led him to decide to hire an expert who has not rendered their final report yet.
Protesters, frustrated with the pace of the investigation, plan to mark the 18-month anniversary of his death by gathering at the site of the shooting Friday night.
They will march to the Mission District Police Station where they will release a letter calling for California Attorney General Kamala Harris to take over the investigation from Gascon.
"I really understand the pain to the family members and the community that want to see a resolution to this case, but I think it is more important to get it right," Gascon said.
He points out some homicide investigations take five or six years to complete.
"A police shooting where there is a death is a homicide investigation and it's important that we do it right," Gascon said.
A loyal group of protesters, activists and concerned community residents have been holding weekly vigils calling for justice for Perez Lopez.
The carpenter and sometime construction worker came to San Francisco when he was 17 to help support five younger siblings and his mother back home.
"He was working about 10 or 12 hours a day, six or seven days a week," said Bill Simpich, a neighbor and a civil rights attorney.
Simpich lives right across the street from where the fatal shooting took place. He took statements from witnesses who saw what happened on February 26, 2015.
He also talked to friends, neighbors and an employer who knew Perez Lopez well.
"He always took his money and sent it back home. And he was really looking forward to having his own bedroom here and still be able to send money to his family," Simpich said.
Simpich says witnesses told him the night of the shooting, a group of men, including a bicyclist were teasing Perez Lopez because he was being evicted. They say he grabbed a knife and chased the men away, but the police had been called. Two plainclothes officers approached him from behind and one grabbed him in a bear hug.
Simpich said, "Amilcar wiggled away and started running because he didn't know who these people were and he was shot."
His friends say he may not have realized they were police officers because he didn't speak English well, it was his third language.
Simpich says an eyewitness he interviewed says the young man was running away and had thrown down his knife when he was shot by the policemen.
But just days after the shooting, then-Chief of San Francisco Police Greg Suhr said: "The suspect, the deceased, lunged at the officer with the knife overhead. He fired five shots. The original initiating officer fired one."
San Francisco Public Defender Jeff Adachi counters, "Witnesses say just the opposite, that he was trying to get away and he was shot in the back."
An independent autopsy shows that six shots hit Perez Lopez from behind, four in his back, one to the arm, and one to the back of his head.
The official autopsy report from the San Francisco Medical Examiner says the same thing.
Adachi says if there were ever a case in which charges against an officer should be filed for a shooting, this is it.
"I've been around for three decades and I've never seen an officer charged in a citizen shooting," Adachi said.
Father Richard Smith of the Episcopal Church of St. John the Evangelist has led the weekly rallies calling for justice for Perez Lopez.
"The community deserves to have our day in court as do the officers who did the shooting. Bring this to court. Let a jury decide," Smith said.
The priest says the evidence shows Perez Lopez was running for his life and witnesses came forward despite fear they could face deportation.
He admits he's frustrated by the delay in the pursuit of justice.
"This has opened a wound for many families here in this neighborhood. This is not an isolated incident. This kind of excessive force, of abuse by law enforcement has been going on in this community for decades," Smith said.
Friday, he will present a letter he signed with other community leaders asking Harris to take over the investigation and bring the case to court.
A spokesperson for Harris told the ABC7 News I-Team they have not seen the request to intervene in the investigation yet so they cannot comment, but the Attorney General will carefully read the letter.
Gascon says he will make his charging decision public, and forward a report to the State Attorney General and the Department of Justice.
Click here for mores stories by Dan Noyes and the I-Team.