We now know more about two teens killed in Biddeford Saturday night. Kari Henderson says her younger brother, Derrick Thompson, was full of life. Police say Thompson and his girlfriend, Alivia Welch were shot and killed by their landlord. It’s believed an argument about rent and winter parking led to the shootings. Thompson’s relatives say they don’t understand why the two were killed about something “so senseless.” “He is 74 years old, he did not have to take two lives that were just beginning,” said Katelyn Grant, Thompson’s cousin. “They had so much to live for. Why? That is what i ask myself. why?.””I do not know how to put it all together,” Henderson remarked. “It is just so hard to accept.”There was a vigil Monday night in Biddeford for friends and families of the victims.