LEWISTON, Maine—Authorities carried out a massive search for an Army reservist wanted for murder in connection with the U.S.’s deadliest mass shooting this year, a rampage that sent shock waves through Maine and left part of the state on lockdown.

Eighteen people were killed and 13 people injured in the attacks Wednesday night, Maine Gov. Janet Mills said. The shootings took place separately at a bowling alley and restaurant about 4 miles apart in Lewiston, a city of 38,500 people 36 miles north of Portland.