Police say the man admitted to shooting the 17-year-old girl, claiming he was frustrated with spotters and poachers in the area.
Delaware officials are urging motorists to watch out for deer crossing roadways.
Officials says shorter fall days, which become even shorter with the end of daylight savings time Sunday, mean more evening commuters driving home at dusk could encounter deer.
Last year, law enforcement authorities reported 1,030 deer-vehicle crashes in Delaware. As of September, 591 deer-related crashes were reported this year.
But officials say even more crashes may have gone unreported to the police or were reported only to insurance companies. State Farm recently reported that motorists made more than 4, 200 deer/vehicle collision insurance claims in Delaware between July 2012 and June 30 of this year.
They also note that about half or more of all deer-vehicle collisions occur during October, November and December.
Delaware isn't the only area state with a big deer problem. Pennsylvania led the nation in deer-vehicle crashes last year, according to a recent study.