HOUSTON (KTRK) -- The brutal killing of a teenager inside a Bellaire pizzeria remains unsolved.A robber shot 19-year old Peter Mielke to death on Sunday evening, February 21st and then calmly walked out of the restaurant, according to investigators.Bellaire detectives said the gunman demanded Mielke open a cash register which he didn't have access to. That's when "without provocation," according to Bellaire police, the suspect shot Mielke several times before fleeing the store without taking any cash or property.Bellaire Assistant Chief Byron Holloway said the suspect calmly walked away from the scene southbound on Ferris St. towards Jessamine. Holloway called the suspect a "coward."Mielke, Holloway said in the press conference, was well-liked by everyone he knew and was "trying to do things right, trying to be responsible," with his work at the pizzeria.Police and Crimestoppers increased the $5,000 reward for information to $10,000.Anyone with information can call 713-222-TIPS. You can remain anonymous.