A string of arsons in Cottage Grove on or near public school property has unfolded in a week’s time, with the charring of a park’s playground equipment the most damaging of the fires.

Playground equipment at Kingston Park, next to Grey Cloud Elementary School, was found on October 23 to be a melted and charred mess from a late-night fire, police said. Officials estimate the damage at more than $30,000.

The next day at the school, a large trash bin outside was set ablaze.

The other suspected arsons came a few days earlier. Two portable toilets were torched on Oct. 17, again at Kingston Park. On Oct. 21, a trash bin was set on fire outside Crestview Elementary School.

A $250 reward is being offered for information leading to any arrest and conviction in these crimes. Anyone with tips for police can call 651-439-9381.

Another Twin Cities suburb, about 40 miles northwest of Cottage Grove, is coping with a similar suspected arson spree that has yet to be solved.

In Andover, fire at Shadowbrook East Park in late September burned a playground structure and caused more than $30,000 in damage. It’s one of six arsons in the city’s parks since June.

“We don’t believe the Andover fires are related to any other arsons,” Anoka County Sheriff’s Cmdr. Paul Sommer said Thursday.

The rash of fires in Andover started with small flames inside garbage bins. Then over the summer and early fall, fires set in Andover parks grew in number and intensity, with the playground blaze being the most recent.

Park officials say an arson tip line set up this month has helped investigators narrow their search for suspects — a notoriously tricky task given how little evidence a fire leaves. Sommer said investigators suspect teens are behind the fires in his county.

The state chapter of the International Association of Arson Investigators is offering a reward of up to $5,000 for tips that result in an arrest in the Andover fires.