This is the correspondence purportedly mailed to the San Francisco Chronicle by the Zodiac Killer, likely mailed on May 6th 1986, due to an unclear postmark.
The author alluded to killing more than one person when he used the word "slaves" along with "They were killed by a freeway", suggesting his attack claimed at least two victims.
Previous confirmed Zodiac attacks had involved the killer approaching the victims car at some point either before or after the attack, in particular the Zodiac Killer's first two crimes at Lake Herman Road and Blue Rock Springs. So with the mention of 'freeway' in this letter, it obviously suggests we should be looking for a scene bearing these hallmarks.
If the letter was postmarked May 6th 1986 (which is a strong possibility), he would have committed this crime, as he stated in the letter approximately two weeks earlier, sometime in the latter third of April 1986.
Exactly two weeks prior to May 6th, on April 22nd 1986, Koy Ien Saechao (48) and Choy Fow Salee (40), a Laotian couple were brutally gunned down by the interchange of Highway 99 and Interstate 5 in Sacramento, California after they had pulled over to take a break. Koy Ien Saechao and Choy Fow Salee were traveling back on the three hour journey to their residence in Dorman Road, Yuba City after visiting their son in a Merced CA hospital, situated in the area of the San Joaquin Valley of Northern California. They were only 45-50 minutes from home when it was believed they had opted to take a rest on the roadside edge, near the interchange of Highway 99 and I-5 Sacramento, and unfortunately for them a ruthless killer was in the vicinity. However without knowing the exact dynamics of the crime it is equally plausible they were ushered to the side of the highway on a ruse, similar to the Modesto abduction of Kathleen Johns.
A short time later a California Highway Patrol Officer was stopped by a hitchhiker in East Nicolaus, informing the officer that he had just witnessed an accident, which led police to the murder scene. The hitchhiker was never traced- but was he somehow involved?
In 2001 Devon Stuart Olson confessed to the murder of the Yuba couple, apparently attempting to provide investigators with details of the crime, however, little connected him to the crime and he was never charged. He also laid claim to 10 other murders. Despite several terms in prison for other offences he was paroled in 1998 and has never been heard from again.
This is a debatable Zodiac letter, as it is a Zodiac crime, but it is without much doubt that the author of the 1986 letter is describing the senseless slaying of Koy Ien Saechao and Choy Fow Salee.