The Longmont Police Department told the newspaper the slashings happened between 1 a.m. and 2 a.m. Sunday in the parking lot of a hotel in the 1400 block of Dry Creek Drive.
There are no suspects.
In the arson investigation, detectives have surveillance video that could identify who set fire to the vehicles and dumpster in central Longmont on Monday morning.
Police are also investigating a June 19 vandalism case in which someone smashed out 12 windows on eight vehicles with a club or bat in north Longmont.
Police said there is no evidence the three cases of vandalism are related.