The cases were different, but the medium was the same.

In one, the man's harassing messages poured in — even after his ex-girlfriend fled Texas for the Twin Cities.

In another, a woman messaged the father of her children moments after she violently attacked him in the apartment they shared, swearing that she would kill him soon.

Both were convicted last year in Hennepin County District Court of stalking and terroristic threats. It's a small victory for police and domestic violence prevention advocates who say they're seeing more cases where abusive domestic partners and stalkers hound their victims across social media sites, sometimes anonymously. The high rates continue even with tough state laws that beef up penalties for cyber-harassment and stalking via social media, e-mail and other electronic communications.

Assistant Minneapolis City Attorney Michelle Jacobson, who heads her office's six-attorney domestic violence division, said part of the problem is that cyber-harassment remains a difficult crime to prove. Messages can't always be preserved, many incidents go unreported and suspects often mask their identities.

"I feel like a fraud sometimes, because it's so difficult to prosecute these people," Jacobson said.

For example, Jacobson said, an offender might post a threat on social media directed at his or her victim while logged in to a public access computer at a library. Even if authorities managed to track down the internet protocol (IP) address of the computer from which the message was sent, they'd have a tough time proving who sent it.

Assistant Hennepin County attorney Jamie Becker-Finn said that cracking down on such crimes is a priority for her office.

From her office at the Domestic Abuse Service Center in downtown Minneapolis, Becker-Finn reviews dozens of cases every month involving unwanted social media contact. Few result in criminal charges, she says, because of insufficient evidence.

"My guess is behind almost every domestic case that we see, there's always some social media involved," Becker-Finn said. Most of the stalking cases are charged based on other electronic evidence, such as voice mails left on a victim's phone, she said.

Going underground

Investigating such crimes can be time-consuming, authorities say.

Even if they can get an internet service provider to cough up an anonymous IP address holder's real name and address, investigators must still obtain a search warrant to inspect that person's computer or smartphone, then send it off to criminal labs for forensic testing — a process that can take weeks, experts say.

"The third piece is, how do we prove the person who has the [order for protection] against him or her typed that message and not their brother," Becker-Finn said. "The biggest thing to me is how often it's occurring and how little we can do about it."

Complicating matters is the growing popularity of anonymous messaging apps like Kik, Whisper and Surespot, which allow users to talk with friends or strangers, without revealing their identities.

Some cases involve spoofing technology and sites like that trick people into picking up the phone when their caller ID shows the name or number of a relative or a co-worker, domestic violence prevention advocates say.

"If you Google the term, 'How to spy on my spouse,' you would be dumbfounded," said Cindy Southworth, founder of the Safety Net Technology Project at the National Network to End Domestic Violence.

"If 90 percent of adults are using the internet, 90 percent of the [stalking cases] involve the internet," she said, citing a Pew poll that found that nearly 90 percent of U.S. adults go online. "The majority of cases have a technology element."

In 2014, authorities say former Highland Park and Visitation high school tennis coach Daniel Erik Hubbard Wilson tricked a teenage girl he was convicted of sexually assaulting into following him on Twitter.

After the girl's father sought a restraining order against the coach, the girl told investigators that someone with a TV character's name as their Twitter handle asked her to follow them on the microblogging site. Sometime afterward, the girl received a tweet directing her to a blog with posts believed to have been written by Wilson, prosecutors said. A Ramsey County judge sentenced Wilson to six years in prison for violating the terms of his probation by continuing to attempt to contact his victim — but only after his third violation of a harassment restraining order in the case.

It's a problem that frustrates domestic violence prevention advocates here and nationally.

Ruth M. Glenn, executive director of the National Coalition Against Domestic Violence, said abusers sometimes skip more traditional forms of communication like e-mail and texting.

"Particularly if they're under a no-contact order, they're going underground," Glenn said. "So they may be using Snapchat, because it's so much harder to trace."

Cases underreported

Eboni Broom, a legal advocate coordinator with the Domestic Abuse Project, said that in a recent case in Minneapolis, a man created several fake Facebook accounts that he used to harass a former romantic partner and her relatives.

Local domestic violence prevention advocate Safia Khan said that while most tech companies cooperate with law enforcement demands if they are supported by a court order, many local departments lack the resources to fully investigate such cases.

While social media has been helpful in prosecuting offenders by providing investigators with a digital evidence trail to follow, it also continues to frustrate advocates. Companies with foreign servers can make it difficult to get a subpoena, she said.

The Dakota County Sheriff's Office is one of the few law enforcement agencies in the state with a special investigative unit that tracks "technology-based violations" in domestic abuse cases. Many agencies with limited resources go after only the most serious cases of domestic violence.

Still, Khan said, despite its prevalence the problem of technology-aided stalking remains underreported.

"A lot of times, women don't think other people will think it's that big of a deal," said Khan, a program manager at the Minnesota Coalition for Battered Women. "The victims sometimes don't believe people will invest the energy into looking into it."