You don’t need to have a gun to commit robbery.  Green Bay police are ramping up efforts to catch a robber using a knife to stick up five businesses in the last three weeks.  All the robberies were on the city’s west side.  Witnesses say the man enters a business late at night, shows his knife, takes the cash and runs off.  It’s possible two similar crimes in De Pere and Ashwaubenon are connected.  Nobody has been injured.  The robber wears a mask and doesn’t say much, so investigators are working with very little evidence.