Union leader charged with causing more than $1,000 worth of damage to school property.

Tracks in the snow led to pickup Diaz was driving, investigators said.

Felony conviction would end the police career.

The president of the Detroit Police Officers Association took the stand in his own defense today, denying he intended any damage at a school where he drove his truck through snow banks and over the grass.

Mark Diaz, 42, of Holly is charged in Oakland County Circuit Court with reckless driving, a misdemeanor, and malicious destruction of property, a felony with a maximum penalty of five years in prison. A conviction on the felony count would end Diaz's police career.

Diaz said he was driving home from his office Dec. 20 in his union-issued pickup truck, which was purchased in July, when he decided to go into the Holly Academy, a charter school near his home.

"I had not tested the 4-wheel drive out on the vehicle," Diaz said. "When I drove past the school and saw other tracks there, recognizing that the ground would be frozen and covered in snow, I foolishly thought that was an appropriate opportunity to check it, to check the 4-wheel drive was working properly."

Investigators said Diaz caused $4,200 worth of damage to a culvert in the grassy area of the school yard. Diaz admitted it was a bad choice, but insisted he didn't know he'd damaged the culvert or any other property. He said the culvert was snow covered and he never saw it.

When asked by Assistant Prosecutor Andrew Starr if he'd been drinking that night, Diaz said no, but said he made a bad choice by driving where he did.

"It was poor judgment, but nothing was affecting my judgment," Diaz said.

A jury of nine women and five men will have the weekend to think over his testimony before they return on Monday to begin deliberations on his fate. Two will be randomly dismissed to reach the required 12 jury members.

Earlier in the day in court, custodian Christine Voich told jurors she was loading trash into a Dumpster when she saw the truck driving through the school parking lot, through snow drifts, over sidewalks and across sections of lawn. The truck was moving so erratically she feared he might hit her.

"I was afraid he didn't know I was out there," Voich said, adding she used the Dumpster to shield herself in case he came her way.

Diaz acknowledged that as an officer, he's testified in court many times. As he was speaking, he frequently turned his head to make eye contact with the jurors and pressed his fingertips together in front of his chest to emphasize certain points.

He acknowledged that the lower half of the truck's front bumper was torn off and left at the school, but said he didn't notice it when he got home and learned about it the next morning when his wife spotted the damage in the driveway.

He said he was embarrassed by the charges and regretted his decision that night.

"This was poorly thought out, it was inappropriate and it was wrong," Diaz's lawyer, James Thomas, told jurors. "He freely acknowledges it and he offered to pay for it. You're going to deal with whether the conduct here was criminal."

To convict Diaz, Thomas said, the jury must conclude his conduct was "willful and knowing," which Thomas said it was not.

Starr disagreed, telling the jury it was willful and wanton conduct.

"He had his hands off the wheel while he is driving wildly and talking loudly on the phone," Starr said.

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Earlier today, Jose Melero, Voich's boss, testified that the morning after the incident, he found damage around the campus, including the culvert that was partially collapsed after the truck went over it. He followed the tracks off campus, down the sidewalk of a neighboring subdivision and to a pickup truck parked outside Diaz's house. The truck was damaged and had one tire removed.

In closing arguments, Thomas told jurors they must find that Diaz intended to harm the school property.

"It wasn't his intention, he told you what his intentions were," Thomas said. "He ran into something that was unseen and unanticipated."

Starr disagreed, saying Diaz's testimony sounded canned and came from a man who had testified many times before.

"His story doesn't make sense," Starr said. "This isn't a 16-year-old, this is the head of the Detroit Police Officers Association."

In addition to being union president, Diaz serves on the Michigan Commission on Law Enforcement Standards, the state group that licenses police officers in Michigan. He also serves as a trustee of Detroit's Police & Fire Retirement System.

Thomas told Judge Leo Bowman on Thursday that he attempted to negotiate a plea deal, but Oakland County Prosecutor Jessica Cooper's office declined. Diaz also agreed to waive his right to a jury and have Bowman decide the case, Thomas said. But Cooper's office objected.

Diaz has been suspended with pay by Detroit Police since February. Chief James Craig had recommended suspension without pay, but the Board of Police Commissioners in March rejected Craig's recommendation.

Contact John Wisely: 248-858-2262 or jwisely@freepress.com. On Twitter @jwisely.