Brianna Kupfer knew something was off with the man who walked into the Los Angeles furniture store where she was working alone. The UCLA grad student texted a friend on Jan. 13 to say there was someone in the store Croft House on North La Brea Avenue who was “giving her a bad vibe,” LAPD Lt. John Radtke said on Tuesday. The unidentified homeless man stabbed Kupfer, 24, in what cops said was “a random act of violence.” Her body was found a short time later by another customer. “This individual responsible for this vicious senseless and brutal crime is walking amongst us,” said LAPD Chief Michel Moore in announcing a $250,000 reward for information leading to the killer’s arrest. Los Angeles Councilman Paul Koretz said he introduced a motion on Tuesday for a $50,000 reward, while the rest of the money came from community members who have donated funds to the Kupfer family. The suspect is described as a tall man with braided hair, wearing a dark hooded sweatshirt, dark pants and black tennis shoes. Cops said he should be considered armed and dangerous. Kupfer’s father, Todd, told The Post investigators are working hard on his daughter’s case. “We are extremely thankful for this show of support and hope it will lead to his capture.” He criticized city leaders and said the recent uptick in crime is because of lenient policies against criminals. Kupfer, of Pacific Palisades, was studying architectural design at UCLA and worked at the store as a design consultant.