41 razor blades were found at a playground in Eaton Rapids, prompting officials to check on parks in the Michigan city out of caution.

Michigan police said in a news release that ‘some of the blades appeared to have been placed intentionally to cause harm.’

On Monday, a group of people found 39 blades around playground equipment at Howe Park. Police and city staff found two more when they searched the park bringing the total number of blades to 41.

Michigan put out an all-call for large, construction-grade magnets to help find and collect any other razor blades that may have been left at other parks in the community. Later on, city workers found more in the grass at GAR Memorial Island.

“Although we have done everything in our ability to ensure the safety of the park spaces, please remember to always remain aware, alert, and diligent about your surrounding,” the city said in a statement.

Witnesses said that they saw four teenagers on the Howe playground equipment before the razor blades were discovered.

The city is offering a $2,500 reward for any information leading to the arrest of the suspects.

“The investigation into this incident is ongoing. There are no suspects in custody,” said Larry Joe Weeks, Eaton Rapids Police Department Chief of Police.