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Using Helianthus annuus Seeds to Solve A Mystery

Name: Supreet Babbar

Student Number: 999739074

Practical Section: 12

Teaching Assistant: Chris Kong-Kee

Submission Date: November 19th, 2012

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Introduction:

Forensic botany is the use of botanical evidence in criminal investigation. The recognition, collection and

preservation of plant materials can play a vital role in determining the manner or time of death. It can also be used

to investigate if the death was accidental, a suicide or a homicide (Coyle et al, 2005). This concept of forensic

botany can be applied to the case of Roger T. Peterson‟s suspicious death. The victim‟s body was found under a

tree behind his store. In addition to the evidence for the blunt force trauma to the body, Helianthus annuus seeds

were found on and around the body (Rush et al. 2012). These seeds were compared to the seeds collected from the

home the prime lead suspect. In order to prove that the suspect was at the scene of crime, it was necessary to

answer the question if the two seed samples collected as evidence were similar. Confirmation or the rejection of

the two seed samples being similar is not enough to prove that the suspect is guilty or innocent. In this investigation

environmental factors such as temperature and moisture were not taken into account, although they have shown to

affect the physical characteristics of Helianthus annuus. Based on other circumstantial evidence collected including

fingerprints of Bobby Walden found at the cash and on the back door, along with his habit of leaving a trail of

Helianthus annuus seeds and his history of petty thefts it is hypothesized that he was at the scene of the crime and

the prime suspect of this case. In addition statistical analysis of the seed samples was also conducted. The

hypothesis is test by comparing the calculated sample t test value to the critical value. If the sample t statistic was

greater than the critical value, this data demonstrates that the two seed samples from the victim and suspect are

different, rejecting the null hypothesis. The hypothesis is test by comparing the calculated sample t test value to the

critical value. If the sample t statistic was lower than the critical value, then this data demonstrates that the two seed

samples from the victim and suspect are the same, failing to reject the null hypothesis.

Abstract:

The purpose of the experiment was to analyze the seed evidence collected from the victim and the suspect

to help solve the murder case of Roger T. Peterson. It was hypothesized that Bobby Walden, the prime suspect, had

a role to play in the death of the victim and had been at the scene of the crime. The circumstantial evidence

targeting Bobby Walden, were his fingerprints found in the store and the trail of his favourite snack, Helianthus

annuus seeds. A total of thirty five seeds each were collected from Bobby Waldon‟s house and from on and around

the victim‟s body. The length (in mm), width (in mm), depth (in mm), weight (in grams) and volume (in mm3) of

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all seeds were recorded and transferred to an Excel spreadsheet. The mean, standard error value, standard deviance,

and variation values were generated through the calculations based on the measured characteristics. In addition, the

sample t statistic values were calculated for the measured characteristic of the seeds collected from the suspect and

the victim. The t statistic values were found to be higher than the t critical value (more than 1.995). This confirms

the rejection of the null hypothesis, indicating that the seed sample characteristics of those of the victim and

suspects were different. Furthermore, it would be unfair to implicate the suspect as having been at the scene of

crime when the victim died, as his seeds did not match up to seeds found at the crime scene.

Method

On the morning of August 15, 2012, at Highland Creek, Roger T. Peterson was found murdered in his pet

store. Helianthus annuus seeds were collected from around the body of the victim and from the house of the prime

suspect, Bobby Walden. The seeds were sent to the Forensic Botany Department at UTSC to help with the

investigation of this mysterious death. A total of thirty-five seeds each were collected and analyzed from the

suspect and of those found near the victim. The botanists were divided into two groups and were provided

randomly with packets of Helianthus annuus seeds. The packet contained six to seven Helianthus annuus seeds. A

marker was used to number the seeds in the packets provided to the forensic botanist to analyze. The botanist used

a ruler to measure the length (in mm), width (in mm) and depth (in mm) of the seeds. The volume was calculated

by using the following formula, V = 4π/3 (length/2)(width/2)(depth/2). The mass of each seed was measured by

using a top-loading balance (in grams). All the measurements were recorded on the “Data Sheet” (Rush et al.

2012). The data of the seeds where transferred to an Excel spreadsheet and the descriptive statistics were

calculated (mean, maximum, minimum, standard deviation, variance etc.). A t-test (Mean 1 – Mean 2|/√ (SEM12 +

SEM22) was constructed to compare the measurement variables (length, width, volume, depth and weight) of the

Helianthus annuus seeds taken from the suspect to those collected from the victim. The t statistic values were

compared to the critical values, in order to determine if Mr. Walden was present at the scene of crime where the

body was found and could be a potential lead suspect in the case.

Results:

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The characteristic of length, width and depth of Helianthus annuus seeds from the suspect and the victim

were compared and analyzed and. The measured characteristics were compared against the descriptive statistics,

which included the mean, standard deviation, minimum and maximum values of both samples (Refer to Table 1).

From this constructed table, the values obtained for length, width and depth of the seeds were shown to have

perceptible different between the victim and suspects seeds. The mean value for length, width and depth were

notably higher for seeds collected from the suspect in comparison to the seeds found on and around the victim. The

maximum and minimum measurement values of the data set for length, width and depth are consistently higher in

the seeds of the suspect than of the victim. In addition, the values for standard in terms of length, width and depth

were larger for the seeds of the suspects in relation to those of the victim.

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Table 1: Measurement Characteristics of Helianthus annuus Seeds collected from the Victim and the Suspect

Length (mm) Width (mm) Depth (mm)

Victim Suspect Victim Suspect Victim Suspect

Minimum

10 11 5 4 2 2

Maximum

18

20 9 10 5 8

Mean

12.26 14.67 7.01 8. 3.74 4.44

Standard

Deviance

1.591

2.03 1.11 1.705 0.785 1.29

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Using Excel, the variance, standard deviation and SEM were calculated for the measurement

characteristics of the seeds found on the victim and seeds collected from the suspect. The student t-test was created

for each of the measurement variables (Table 2). From the experiment, the degree of freedom for length, width, and

depth was calculated as 68. Subsequently, the „critical t‟ at p=0.05 was determined to be 1.995. The value of the

„sample t‟ was constructed for each of the measurements described above. The values of the „sample t‟ for each

characteristic were interpreted and were found to be notably higher than the value of critical t. This led to the

rejection of Ho (null hypothesis).

Similarly a statistical test was also conducted for weight and volume (Table 3). The degree of freedom for

both variables was calculated to be 68. In addition the critical value remained the same as 1.995. For both

measurements the „critical t‟ value was notable smaller than the sample t value, resulting in the rejection of the null

hypothesis.

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Table 2: t -Test Analysis for Measurements (Length, Width, Depth) of Helianthus annuus collected from the Victim and the Suspect

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Table 3: t Test Analysis for Measurements (Volume, Weight)of Helianthus annuus Seeds Collected from the Victim and the Suspect

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Moreover, the means of the volume and weight of the seeds were graphed to compare the finding of the

victim to the suspect‟s seed. Figure 1 demonstrates the mean volume (mm3) of the suspect and victim seeds, along

with respective error bars representing one standard derivation of the mean. Through this representation, it is

demonstrated that the mean of the suspect seeds are much higher in contrast to the seeds collected from the victim.

In addition, the standard deviation of the suspect‟s seeds mean volume was significantly larger than the deviation of

the victim‟s seeds mean volume. Figure 2 demonstrates the mean weight (in grams) of the seeds from the suspect

and the seeds collected from the victim, along with respective error bars representing one standard derivation of the

mean. The mean weight of the suspect‟s seed was noticeable higher than victim‟s seeds. Furthermore, the standard

deviation of the mean weight of the seeds collected from the suspect was also larger than the deviation of the mean

weight of the seeds from the victim.

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Figure 1: The mean volume of Helianthus annuus seeds collected from the victim and the suspect. The Error bars

represents one standard deviation of the mean (N=35 seeds)

Figure 2: The mean weight of Helianthus annuus seeds for victim and suspect. The Error bars represents one

standard deviation of the mean (N=35 seeds)

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Discussion:

The sample t statistic for each measurement of the Helianthus annuus seed was found to be more than the

critical t statistic value, rejecting the null hypothesis. This implies that the seed sample of the victim and of the

suspects do not show any correlation between each other. Since the seed samples of both suspect and victim vary in

length, weight, volume, depth and width, it can be concluded that Mr. Walden was not present at the scene of the

crime. Therefore, the results do not validate the hypothesis. There are external factor that influence may have

contributed to the errors in calculating dimensions and mass of the Helianthus annuus seeds. For instance,

carbonization, a process that involves an increase temperature, aids in preserving plant parts has been known to

alter the dimensions (length, width, height) and mass of sunflower seeds (Braadbaart et al, 2007). The seed samples

used in the study may have been exposed to various unaccounted for environmental conditions, including variations

in temperature and moisture content of air (humidity); which may have affected their physical characteristics.

Correction factors need to be applied in order to determine the accurate dimensions of the seeds. It is also possible

that the seed evidence may have been depreciated, dried, molded, creating alterations in its initial form (Coyle et al,

2005). Consequently, the dimensions of the seed may have been altered. Another implication that may have caused

errors in the resulting data is the moisture the seeds were exposed to. The bulk density of Helianthus annuus seeds

decreases with the increase in moisture content (Gupta et al. 1996).

Potential errors encountered during the experiment include parallax error while taking measurements. The

instrument used for measurement was not accurate for lengths less than one millimetre. Additional information for

this research could be acquired through more sophisticated means such as microscopy to see the finer details on the

seeds and also using plant DNA testing (Coyle et al, 2005). To conclude, the sunflower seeds collected from the

body do not prove that Bobby Walden had been present at the scene of the death of Mr. Peterson. The analysis of

the Helianthus annuus seed evidence showed that the seeds found near the body were different than the seeds

collected from Bobby Walden. Overall the size measurements were larger for the seed samples from the suspect as

compared to the victim. As larger seeds are used for human consumption and smaller seeds are for pets (birds etc.),

it is very likely that the seeds found near the body were from the bird feeder found near the body.

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Citations:

Braadbaart F, Wright P.J. 2007. Changes in Mass and Dimensions of Sunflower (Helianthus annuus L.) Achenes

and Seeds Due to Carbonization. Economic Botany. 61 (2): 137-153

Coyle HM., Lee CL, Lin WY, Lee HC, Palmbach TM. 2005. Forensic Botany: Using Plant Evidence to Aid in

Forensic Death Investigation. Croat Med J. 46(4):606-612.

Gupta R.K., Das S.K. 1996. Physical Properties of Sunflower Seeds. J . agric . Engng Res. 66(1):1 – 8

Rush S, Gladilina E, Olavasen, M, and Marushia R. 2012. BIO A01-Introductory Biology Lab Manual for Fall

2012. Toronto, Ontario: University of Toronto Scarborough Printing Services. pp. 33-38.