First it was Allen and Patricia Prue accused of kidnapping, assaulting and killing St. Johnsbury Academy teacher Melissa Jenkins.

Just last week, Stephen Howells Jr. and Nicole Vaisey were charged with kidnapping two young Amish girls in the North Country.

Forensic psychologist Tom Powell, who spent more than a decade working for the Department of Corrections in Vermont, said cases like these are often planned out, at times even rehearsed, and the relationships are often based on something much darker than love.

“They see this as a viable way to strike back at the world,” Powell said.

Powell believes when couples are accused of crimes like the abduction of the two Amish girls from their Oswegatchie, New York, farm last week or in the kidnapping and killing of Melissa Jenkins back in March of 2012, it's likely a significant amount of planning went into the crime.

“Through either enactment of fantasies in the privacy of their own home use of pornography that might be on point to what their deviant interests might be,” Powell said.

Police arrested Howells and Vaisey charging them with taking the 7- and 12-year-old Amish sisters.  The St. Lawrence County District Attorney now says the girls were sexually assaulted and more charges are likely.

"There was a lot of thought process that went into this. They were looking for opportunities to victimize,” St. Lawrence County Sheriff Kevin Wells said.

Vaisey's lawyer has said she was in an abusive relationship with Howells and, "She appears to have been the slave and he was the master."

“You know you see one person who stokes an idea and over time it takes shape,” Powell said.

Powell said there's often one dominant force when it comes to crimes committed by couples and it doesn't always have to be the man.

“Oftentimes, the motivation that they have is one of controlling the other to do something bad,” Powell said.

In the case of Patricia and Allen Prue, Patricia is facing harsher charges.

The husband and wife have pleaded not guilty to charges stemming from the death of Jenkins.  Court paperwork shows, detectives believe the couple began conspiring to kill the 33-year-old at least a month before the alleged attack, buying a prepaid cellphone and stun gun and noting a search on Patricia’s computer about “how to kidnap a girl.”

We wanted to know how it could be possible to convince someone to commit a crime, especially when it comes to the magnitude of the charges against these two couples.

“I think it's rooted in a lot of negative relationship issues. Anger being one of them, power being another and frustration.  There's usually a pretty high level of frustration in the world,” Powell said.

The couple was charged with first-degree kidnapping in the Amish girls’ disappearance, Howells and Vaisey, entered no plea during their arraignment.

They are expected to be back in court again on Thursday.