BOULDER, Colo. -- Police say someone mailed ammunition and a threatening letter to a Boulder couple who laid claim to part of their neighbors' land under an obscure Colorado law.

A package sent to Richard McLean and Edith Stevens contained a shotgun shell, a rifle shell and a letter telling them to choose which they wanted to face.

The couple say the package arrived in December. An affidavit unsealed on Thursday revealed what was in the package. Police said this week they found no fingerprints or DNA on the package and have closed the investigation without arresting anyone.

A judge awarded McLean and Stevens about one-third of their neighbor's lot under the law of "adverse possession," which allows someone to gain possession of property after using it unchallenged for 18 years.

The neighbors have appealed.