Identification of stolen rare palm trees by soil morphological and mineralogical properties

The San Diego County District Attorney's office requested our help to investigate the theft of palm trees from a private collection of exotic plants. Circumstantial evidence led investigators to the suspect's residence where 33 palm trees were found. Because the victim raised all palms from seed in the same potting mix, we compared morphologic and mineralogic properties of soil samples collected from the root balls of palms that were at the victim's and suspect's residences. Analyses of soil color, reaction with dilute hydrochloric acid, particle size, heavy:light mineral ratios, and mineral speciation of the >2.86 g cm^-3 fine sand fraction, indicated that 25 of 33 soil samples collected from palm trees at the suspect's residence were very similar to soil samples from palm trees at the victim's residence. After a pretrial hearing at which the soil evidence was presented, the suspect changed his innocent plea to guilty.