DENVER (AP).- Investigators are trying to determine why a woman caused $10,000 worth of damage to a large expressionist painting at the Clyfford Still Museum by punching and scratching it, then removing her pants and sliding down the artwork. Carmen Tisch, 36, faces charges of criminal mischief in the Dec. 29 attack on the painting, said district attorney spokeswoman Lynn Kimbrough. The painting, referred to as 1957-J-No. 2, is valued at more than $30 million. The large montage of black, white and burnt orange swaths with a sliver of yellow is from Still’s middle period. Museum officials said they believe security is adequate for the facility and that they regularly evaluate security to protect the collection and visitors. Museum spokeswoman Regan Petersen said in a statement that its guards “acted swiftly and appropriately; the police were summoned immediately and the offender was taken into