One night this week in a Northwest Washington neighborhood, it may not have been a case of the criminal returning to the scene of the crime. It seemed more a matter of the criminal staying around to keep committing more crimes. Between Wednesday evening and Thursday morning in a section of the Mount Pleasant area, D.C. police said, at least nine thefts from cars were reported. Police have said it is difficult to stop such thefts, which occur quickly and at times when there is little chance of being seen. They recommend locking cars and hiding or removing valuables. This week's thefts occurred in a tree-lined residential area of about a dozen blocks, between Kilbourne Place on the south and Ingleside Terrace on the north. Of the nine or more thefts, the largest number, three, was reported on 19th Street, and two more were reported on Monroe Street. Most were discovered about 8 or 9 a.m. Thursday. The value of items taken in each case appeared to be less than $1,000.