If there is a smoking gun in the Robert Durst murder case, some would argue it's the now infamous letters in which Beverly Hills is misspelled as "Beverley Hills."
But how reliable is handwriting testimony in court?
The final episode of a six-part HBO documentary about Durst -- who was charged Monday with the 2000 murder of friend Susan Berman -- focuses on a writing sample from him.
The episode highlights similarities between an envelope from a letter he sent to Berman in 1999 and an anonymous note sent to Beverly Hills police at the time of her killing, telling them that they would find "a cadaver" in Berman's house.
Both writing samples are written in all capital letters, and in both cases the "Beverly" in Beverly Hills is misspelled.
Handwriting expert Sheila Lowe called the common misspelling "very significant" – especially when combined with other similarities she spotted in the texts.
Lowe, president of the American Handwriting Analysis Foundation, said she'd seen the writing samples from the documentary posted online and thought there was "a strong probability" that both samples were written by the same person.
In both cases, she said, there were Ls with a little curve at the bottom, calling it "a point of comparison." There are also E's in both samples in which the top cross bar is longer than the bottom cross bar and Ss in which the bottom part bulges larger than the top part.
Handwriting has played a big role in some cases.
In the Ennis Cosby murder case, prosecutors used incriminating letters they said were written in jail by the defendant. A prosecution expert witness said the letters were authentic, but the defense contended that the letters were forgeries.
In 1997, the distinctive signature of a defendant became a central part of her murder case. Ventura County prosecutors argued successfully that Diana Haun signed personal checks to buy items such as a wig, pantsuit and camping ax prior to the kidnap-slaying of homemaker Sherri Dally.
But Mark Denbeaux, a law professor at Seton Hall University who has researched handwriting evidence, said he often testifies against its reliability in court.
"It's so bogus," he said. "It's sort of like the emperor has no clothes."
If law enforcement in Los Angeles is "trying to look at letters and shapes and say these two letters are written by the same person," he said, "they have enormous problems."
Comparing handwriting samples is problematic for several reasons, Denbeaux said, noting that each individual's handwriting fluctuates. "Every time we all pick up a pen," he said, "we write differently."
Follow @marisagerber on Twitter.