ROYAL OAK, Mich. -

The Royal Oak Police Department was evacuated Tuesday morning when a detective opened a letter that contained a white powder.

It turned out to be cornstarch.

Police Chief Corrigan O’Donohue said about 25 people in the building were evacuated as a precaution while a hazmat team tested the substance.

"The hazmat team determined that the substance was most likely cornstarch," O’Donohue said.

While the detective was initially being held for any potential medical treatment he might need, O’Donohue said the detective was released after the test results.

"We take this very seriously," O’Donohue said. He said the letter came in the mail and was addressed specifically to the detective, who was not named.

The building had been closed to the public during the evacuation and all 911 and police business calls were transferred to Madison Heights dispatch, but everything was back in place around 10:30 a.m.

Mayor Jim Ellison said situations like this can't be taken lightly.

"We take it seriously, yeah. You don't fool around. I mean, we've heard of these reports before, you never know what crazies are out there and who knows what they're gonna do and what their beef is. Something like this, yeah, you jump on it immediately. You don't take any chances," said Ellison.