An 18-year-old Lowell man died Sunday after he was shot in the head hours earlier in Lawrence, authorities said. Police found Richard Bonilla outside in the area of 400 Broadway in Lawrence at about 1 a.m., city police Chief John Romero said. Bonilla was transported to Beth Israel Deaconess Medical Center in Boston, where he died at about 4:30 p.m. Investigators believe Bonilla was shot by an unknown male who pulled out a gun after a verbal altercation escalated outside a party, Romero said. The dispute was allegedly supposedly over one group of people not being allowed into the party. It was the second homicide in Lawrence this year, Romero said. No arrests have been made.