PORTLAND, Ore. » For about six months, somebody armed with what resembles a small ice pick has been puncturing tires in Portland neighborhoods and otherwise vandalizing vehicles at a rate of 30 to 40 a week.

Police say the number of vehicles has topped 500, the damage may be as much as a quarter of a million dollars, and the crime wave has them stumped.

The slasher or slashers use something like a tiny ice pick, tire store employees told The Oregonian newspaper, so the air escapes slowly. Victims thought they had slow leaks until they noticed all their other neighbors had slow leaks, too.

"That was probably the most frustrating thing for customers," said Joe Petrjanos, manager of a Les Schwab store. "They assumed they ran over something. When you say, ‘No, your tire has been vandalized,’ it’s a shock for them."

Punctured sidewalls can’t be patched, and neighbors have reported spending up to $1,000 after repeated hits.

Neighbors also reported keyed cars and sliced convertible roofs. Some reported whole squares were cut from motorcycle seats.

Portland police detectives aren’t sure if the vandalism is the work of a man or a woman, if it’s a group or someone working alone.

The slashing has moved from neighborhood to neighborhood, some rough and some affluent, with no pattern, police say. Sometimes one or two cars in a neighborhood escape slashing. Sometimes a car gets vandalized a second, third, fourth — and in a few cases, fifth — time.

"I’ve never seen anything like this," Portland police Sgt. Greg Stewart said at a Grant Park neighborhood meeting.

The Police Bureau has offered a $1,000 award, assigned an analyst to work nearly full-time studying the damage, and assigned detectives who normally work on the most serious violent crimes.