A 29-year-old New Haven resident arrested for a spate of East Haven armed robberies has confessed to the Friday afternoon mugging of three Yale graduate students on Humphrey Street. Police charged Michael DeMartino of 1 Brewery Square with criminal intent to commit robbery in the first degree on Saturday. This was not DeMartino’s first offense; he has been found guilty of larceny and narcotics possession multiple times since 2001. He was most recently convicted in 2007 for refusing to show motor-vehicle license and registration. In response to recent street crimes in East Rock, Yale Police Department Chief James Perrotti announced Sunday the introduction of the “special street crimes unit” into the East Rock area.