Wichita Falls police say a man is cooling his heels in the Wichita County Jail after trying to steal cold hard cash from a convenience store.Police say the incident happened around 6:20 this evening at the Quick Stop in the 2100 block of Holliday. According to police, a 30-year-old white male walked in ... grabbed two beers ... put them on the counter ... threatened the clerk and demanded $20. A short time later, police say the same man went to 23rd street and encountered a man on a bike. And again... as police tell it ... this time, the man displayed a knife and demanded cash. Police say he's under arrest, facing two counts of aggravated robbery.