Authorities in Miami arrested a man Saturday thought to be responsible for an armed carjacking last week in the parking lot of a St. Petersburg Best Buy store. Angel Enrigue Martinez, 18, of St. Petersburg, was driving the stolen 2007 maroon Lexus sedan at the time of his arrest, police said. The Jan. 15 carjacking was at the Best Buy at 6600 22nd Ave. N. The victim, a 64-year-old man, was accosted at gunpoint by a robber while leaving the store, police said. The robber told the man to get into the passenger side of the car, but he fled back inside the store. A second man then ran to the car and got into the passenger side before they left, police said.Miami-Dade police arrested Martinez on a warrant for an armed robbery in St. Pete Beach. Those details were not available Wednesday.