CONCORD, N.H. — Spouses or business partners can be convicted of stealing even if they have a joint interest in property taken, the N.H. Supreme Court ruled unanimously Tuesday.

The court upheld nine theft convictions against Karen Gagne, 58, of Andover.

She was convicted in 2011 and sentenced to 10-20 years in prison for stealing hundreds of thousands of dollars from Alice Jane Fair of Concord between 2007 and 2009. The two started a joint checking account in 2007 with the understanding that Gagne would help Fair pay her bills.

The ruling provides guidance to police officers and other investigators in exploitation cases and offers an important safeguard for victims, Senior Assistant Attorney General Jeffrey Cahill said.

Prosecutors established in 2011 that Gagne directed Pleasant View nursing home in Concord to deliver Fair’s bills to her and she assured administrators she would pay the bills. Pleasant View were about to take legal action against Fair in 2009 because her account was so delinquent.

Prosecutors say Gagne used Fair’s money to pay her own bills and buy a home.

Fair died June 30.