Kathryn Sinkevitch (PCSO)


Monday, Kathryn Sinkevitch’s first-degree murder trial entered its fourth day with the testimony of Matthew St. Clair of the Phoenix Police Department Trace Evidence Section of the crime lab.

Sinkevitch is accused in the shooting death of 31-year-old Michael Agerter on Dec. 16, 2016. Agerter, her ex-boyfriend, was shot and killed in the garage of his rental home in Rancho El Dorado. The two lived separately but had an infant son together.

St. Clair positively linked gunshot residue to two black hoodies found in vehicles investigators believe were used by Sinkevitch in the commission of the murder. St. Clair analyzes gunshot residue, foot prints and tire tracks, etc., for criminal investigations.

When analyzing gunshot residue, he examines compounds in the bullet’s primer. The primer creates an explosion and expels particles, which are left on hands, clothing and fabric. The compounds are unique to the primer.

“If we find these particles on hands, they have been using a firearm recently,” he said.

St. Clair tested one of the black hoodies in this case July 20, 2017. He sampled the left and right pocket, cuffs and sleeves of the hoodie to test.

He said he found numerous particles on the right and left side of the hoodie but only one “characteristic particle residue” that was directly linked to gunshot residue on the garment.

“This hoodie was in the vicinity of a firearm when it discharged or touched something with GSR on it,” since the hoodie’s last thorough cleaning, St. Clair said.

A second black hoodie was tested July 24, 2017. There were some residue particles on the right and left but not as many as on the other hoodie, St. Clair testified. It had similar particles on it.

Under cross examination, St. Clair said he can’t determine what type of gun left the residue and can’t determine caliber of the weapon. He admitted only “characteristic particle residue” directly linked to a gunshot was found on each hoodie.


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