A Milford man who police said tried to use a fake prescription to buy a painkiller was foiled because the pharmacist knew the doctor's signature was forged, police say. Dennis M. Decosta, 33, repeatedly insisted the prescription for oxycodone, a powerful opiate, was given to him by his doctor, but the doctor said he has not seen Decosta for more than a year, according to a police report filed in Framingham District Court by Officer Chris Burrell. On Wednesday at 2:15 p.m., the pharmacist from the CVS near Temple Street called police and said a man was trying to pass a forged prescription. Burrell stopped Decosta as he was leaving the store. "He denied that he had been to the pharmacy counter," wrote Burrell. "I then asked him if he tried to fill a prescription inside the store. He denied trying to fill a prescription." However, the pharmacist identified Decosta as trying to use the fake prescription. The pharmacist told police that the prescription used the name of a doctor he knew and he knew the signature did not match the doctor's. Burrell said the pharmacist called the doctor, who confirmed that he did not write the prescription and had not seen Decosta for more than a year. "Confronted with this information, Mr. Decosta admitted that he had passed the prescription but he insisted it was legitimate," the officer said. Decosta said the doctor gave him the prescription three weeks ago, and the doctor always gives him several of the pr ...