A St. Paul police homicide investigator testified Thursday morning that he asked a police commander to secretly obtain a DNA sample from a fellow officer who was dating a purported gang member under investigation for three shootings.

Sgt. Tim McCarty said in Ramsey County District Court that he instructed the commander to retrieve a drink bottle used by officer Ruby Diaz on Feb. 20, 2014 at a meeting at a West Side community center. Diaz was dating Ramone D. Smaller at the time, a purported gang member who is on trial this week on 10 felony counts for shootings in late October 2013.

DNA samples were collected from several individuals to compare their DNA with samples collected from a handgun recovered in a rental car Smaller drove at the time of the shootings. (No one was injured in the shootings.)

Diaz, 39, began dating Smaller, 22, in 2013. She was convicted in December of identity theft for using her best friend's identity to send Smaller $1,500 in prison in 2014. Diaz, who was a school resource officer at the time but has worked as a gang investigator, was fired from the department after her conviction.

Assistant Ramsey County Attorney David Miller asked McCarty if he collected a Buccal swab kit from Diaz, which is typically obtained from suspects and others by swabbing their inner cheek for DNA. Such DNA samples are often collected by executing a search warrant on the person.

"It wasn't appropriate," McCarty said of following that process in collecting Diaz's DNA.

McCarty testified that he instructed a commander to attend the meeting in February 2014, watch Diaz and collect whatever bottle she disposed of. He testified that he delivered the bottle to the Minnesota Bureau of Criminal Apprehension (BCA) for testing.

Miller asked if he labeled the sealed bag containing the water bottle with Diaz's name.

"I did not," McCarty said, adding that he labeled the bag "known sample from an unnamed person."

It's unclear if Diaz has since become aware of the incident. She testified Wednesday at Smaller's trial, admitting that she had rented him two cars that he drove during the time period police believe he was involved in the shootings.

Testifying at her own trial in December, Diaz sobbed and said that she had suffered wide-spread harassment from fellow officers when she dated a different felon before Smaller, and that she did not want her department to discover her relationship with Smaller. Diaz said that officers followed her in unmarked cars, flooded her car with their headlights and refused to back her up on calls when she was a gang investigator.

Diaz was a school resource officer at Humboldt High School in St. Paul when she first met Smaller as a 12-year-old seventh grader. The relationship turned romantic after he turned 21, she has said. Diaz's attorney has said that she is no longer involved with Smaller.

BCA forensic scientist Allison Dolenc testified Thursday that Diaz's DNA was not found on DNA swabs of the gun police believe was used in the shootings. Smaller was the predominant DNA contributor to swabs of the gun's grip and trigger, which also contain a DNA mixture of three or more people, Dolenc said.

Smaller's attorney, Christopher Zipko, has told jurors that the DNA mixture and the fact that no witnesses have identified Smaller at the shooting scenes raise enough doubt to acquit his client.

Testimony in Smaller's trial resumes this afternoon.