Oyamada, 24, was crossing 40th Avenue in Queensbridge on Feb. 21 when he was fatally struck by an NYPD car that was responding to a 911 call.
His family says they've received little information about what happened to their son that night, and now they're appealing to eyewitnesses, asking anyone who was there and willing to offer their testimony to come forward.
"We just want to know the truth," said Chie Oyamada, the victim's mother, in a statement released by the family's lawyer on Wednesday, which marked the six-month anniversary of her son's death.
"A member of our precious family was taken away by the NYPD and they do not give us the right to know the truth. This is very unfair," she said.
"It is unbelievable that this is the reality of New York, the city everyone all over the world visits with big dreams."
Oyamada's family filed an $8 million lawsuit against the city in May.
They believe the squad car that hit Oyamada had been speeding and question whether it had its lights and sirens on before the crash occurred, according to the statement.
The City's Law Department said it could not comment on the lawsuit, citing pending litigation. The NYPD did immediately respond to a request for comment.
Oyamada's family is seeking access to details of the NYPD's own investigation of the accident, the autopsy report, and surveillance video from the scene, but their requests, formalized in the suit, have gone unanswered, they said.
"The story of Ryo Oyamada is not one of a faceless stranger. He was a loving son, brother, and friend," the family's attorney, Chris Fitzgerald, said in a statement.
Oyamada had moved to New York just a few months before his death to study English, the family's previous lawyer told DNAinfo New York.
"What happened to him could have happened to any innocent pedestrian," Fitzgerald said in a statement.
"It is in the best interest of all New Yorkers for the witnesses to this tragedy stand up for what is right and come forward to offer their testimony."
Ryo Oyamada's family is asking anyone with information to contact the Law Office of Christopher H. Fitzgerald at (646) 580-3489 or CFitzgerald@CHFLegal.com.