The last time Dawn Momohara’s mother heard from her daughter, she told her she was going to meet friends at a shopping center in Honolulu.
Hours later, after Dawn, 16, didn’t return home that Sunday afternoon in 1977, she was reported missing, The Honolulu Star-Advertiser later reported.
The next day, March 21, 1977, just before students began Monday morning classes at McKinley High School, Dawn was found dead on the second floor of what was then called the English building. She was partially clothed and an orange cloth was tightly wrapped around her neck.
The police determined at the time that she had been strangled and possibly sexually assaulted, but a suspect would not be identified for decades.
On Tuesday, nearly a half-century after Dawn’s body was found, Gideon Castro, 66, was arrested and charged with murdering her, said Honolulu Police Department Lt. Deena Thoemmes at a news conference. Mr. Castro graduated from McKinley High School in 1976 and knew Dawn.
Mr. Castro was identified after a six-year investigation during which modern D.N.A. testing technology helped match evidence at the crime scene with his D.N.A., the police said.
In the days following the murder, Mr. Castro and his brother, William, were questioned by the police along with numerous other classmates. Mr. Castro told police then that he had met Dawn at a school dance in 1976. He said his last interaction with her was at a school carnival in February 1977, when he told her he was in the U.S. Army Reserve.
His brother William told the police that he had met Dawn through his brother. Neither was a suspect at the time.
The only lead the police had early on in the investigation was a description of a man and a car that were seen by a witness in the high school parking lot on the night Dawn’s disappeared. In the weeks after her death, Honolulu police stopped and checked all vehicles that looked like what the witness described as a maroon and white Pontiac sedan, according to a 1977 article in The Star-Advertiser.
The police also canvassed the neighborhood, carrying around photographs of Dawn and asked residents if they had seen her on the Sunday she left to go shopping, another article said. It wasn’t clear whether she ever made it to the Ala Moana Center, where she told her mother she was going to meet with friends.
The case went cold for decades until 2019, when detectives in Hawaii re-investigated Dawn’s murder with the help of modern D.N.A. testing technology. Using D.N.A. evidence found on her shorts in 1977 and the more-advanced technology, the police were able to identify both Mr. Castro and his brother, William Castro, as potential matches.
Starting in 2023, Lieutenant Thoemmes said, the investigators went to Illinois and Utah to secretly obtain D.N.A. samples from the adult children of the Castros to pinpoint which of the brothers’ D.N.A. was found at the crime scene. After tests excluded William as a potential suspect, investigators obtained Gideon’s D.N.A.
Gideon Castro’s D.N.A. eventually matched, the police said. He was arrested at a nursing home in Utah on Tuesday and charged with second-degree murder. It was not immediately clear if he had legal representation.
Lieutenant Thoemmes said that both federal and local law enforcement officers were involved in the “tireless pursuit of justice for Dawn and the Momohara family.”
Kirsten Noyes contributed research.
