The gun was found in less than a foot of water at low tide at 5:30 Friday morning. It contains the same serial number as one purchased by Goh earlier this year. ABC7 News has learned Goh legally bought a gun at the Bullseye Gun Shop in Castro Valley.
The moon played a big role in the discovery. The canal the gun was found in is relatively shallow. The water depth can fluctuate by four or five feet. When the tide goes out, especially during a full moon, much of the bottom is exposed.
"It was a waxing moon at this point so you're going to see this large coefficient existing and just a big shift in the tides," said Liz Taylor, a marine expert from Alameda.
"Since it's such a shallow body of water in that particular region, it's even more evident when the tide moves out, you see these big expanses of mud open up," she added.
The gun was found along the route police believe Goh used to drive from the shooting scene to Alameda Monday.
The discovery comes after an exhaustive, around the clock, multi-agency search that included 25 divers from Alameda County's Office of Emergency Services and the use of sonar equipment from the Coast Guard and San Francisco Marine Unit.
In the end, it was a relatively small team of Oakland investigators walking in the water with flashlights who found the gun.
There are numerous witnesses who have identified Goh as the Oikos shooter, and the suspect has made incriminating statements, but having the murder weapon could be an important piece of evidence at trial.
Robert Talbot, a professor at University of San Francisco School of Law, said: "These days with the prevalence of crime scenes investigations on television, they like to have some kind of forensic evidence, some kind of ballistic evidence, tying the suspect to the murders.
"Even though there are eyewitnesses you can never really be sure what eyewitnesses are going to be saying, particularly under the high stress situations that many of them were under."
According to Talbot, the gun could also be important at trial in terms of undermining an attempted mental defense or claim of insanity. The prosecution could argue by throwing the gun in the water, Goh was trying to hide it, which would indicate he knew right from wrong the day of the shootings.
