Dr. Cheng - Tidal Evidence

Anyone familiar with the Scott Peterson trial knows that tidal evidence, as presented by Dr. Ralph Cheng, played a significant role in Scott's conviction.  It's not that he was needed to prove that Laci was in the Bay, but to prove no one else put her in the Bay, only Scott could have put Laci in the Bay.

The Prosecutors knew there was a likelihood that Scott's defense lawyer, Mark Geragos, would argue that someone else killed Laci and put her where it was widely publicized that he had been on the 24th -- fishing along a route from the Berkeley Marina to Brooks Island.  So the killer(s) simply put her body there. 

The Prosecution also likely knew that the killer(s) wouldn't need a boat to put her in the area that would naturally incriminate Scott.  Indeed, there are numerous places along the shoreline from the Berkeley Marina to Richmond that a car could have pulled up alongside the shoreline and simply dumped a body in.  And there are places along that shoreline with very large riprap and other debris on which a body could get caught and be concealed from public view.  Especially at the Albany Bulb. 

Where ever she washed ashore, whenever she washed ashore, the police, the media, and the public would conclude that Scott was guilty. 

How do I know they likely knew these things?  Because I assume they had the intelligence to anticipate arguments from the defense and be sure they could counter them.  So they would investigate the area themselves to see if there was another way Geragos could argue the bodies could have gotten into the Bay.

Dr. Cheng's role was to show that the bodies came from Scott's fishing route, not somewhere along the shoreline.  He first had to explain why it took so long for the bodies to wash ashore.  He said it was a combination of strong winds on April 12, 2003 concurrent with a negative low tide that caused the bodies to dislodge and begin moving towards shore.

In his words,  "wow, quite a wind event during that day. I really recall in my own mind, you can see now the scientific records showed us now during that particular period of time, in the morning, or starting from the midnight of the midnight April 11th, or early morning of April 12th, you can see wind exceeded 40 knots. 40 knots, wind exceeded. Also a sustained wind for long period of time, subsided slightly, but still continued on for another good twelve, eighteen hours with wind average around twenty knots per hour. So that is quite a magnitude of wind. And during that period of time, there was occurrence of a very low tide right after noon of April 12th."  

Let's look at the 3 elements of his argument for this "wind event" on April 11-12:

• Wind exceeded 40 knots
• Sustained winds of average 20 knots for 12-18 hours
• Concurrent with the very low tide right after noon of April 12

I fact-checked Dr. Cheng's claims by surveying 11 area weather stations that measured wind and had their data online.  I also copied a graph of the tide on April 12 from the NOAA Richmond station to compare with the wind data. I started with the wind stations closest to where the bodies washed ashore and spread out from there.  I surveyed: 

1. the NOAA Richmond Station,
2. the UC Richmond Station,
3. the East Bay Municipal Utility District station on Point Isabel, 
4. the Oakland North RAWS (Remote Automated Weather Station),
5. the wind station at the Berkeley Marina,
6. the wind station on Angel Island,
7. the wind station on Treasure Island,
8. the Oakland South RAWS (Remote Automated Weather Station),
9. the NOAA Alameda station,
10. the wind station on Crown Beach in Alameda,
11. the Oakland Airport weather station

Not a single one of these 11 stations verified Cheng's claims.  Why was it necessary to exaggerate and misrepresent that "wind event" on April 12?  Because the truth didn't cut the mustard.