The memorial for Alex Pretti, who was shot and killed by federal agents on Jan. 24, has grown to span several parking spots on Nicollet Avenue in the Whittier neighborhood of Minneapolis. It’s now a mountain of carnations, prayer candles, poems, and notes. One message pleads: “America, do not let their deaths be in vain - We the People.”  Alex Hand, a 40-year-old caregiver, knelt down to place a bundle of lilac and maroon satin flowers at the site on a recent morning. “Alex Pretti stood up for