Jason Anthony Bulmer and Morgan Lane Arnold

Jason Anthony Bulmer (19) and his girlfriend Morgan Lane Arnold (14) have been charged as adults with first- and second-degree murder and conspiracy to commit murder in the stabbing death of Howard County blogger Dennis Lane. (This photo was taken from a Facebook page linked to the two suspects and confirmed by fellow students. / May 10, 2013)

A prominent Ellicott City blogger and businessman was stabbed to death by his daughter's 19-year-old boyfriend, who plotted with the 14-year-old girl to kill him so the two could run away together, Howard County police said Friday.

Dennis Lane, 58, was found before dawn in his Winding Ross Way home. Police charged Jason Anthony Bulmer and Morgan Lane Arnold, both students at Mount Hebron High School, as adults in his killing; they both face conspiracy and murder counts. Both were held without bail, according to online court records.

Police said Arnold and Bulmer, who had blood on his hands and clothes, were found sitting in an upstairs bedroom when officers arrived and found Lane dead in a second bedroom. Another adult resident had heard a commotion and called 911.

The killing astonished residents of the close-knit community and those who said the father and daughter were devoted to each other. The scenario described by police was equally unfathomable: Arnold encouraged Bulmer to stab her father and told him they would run away together afterward.

But a motive remains unclear, police said.

"We really at this point don't know why they wanted to hurt or kill Mr. Lane," said Sherry Llewellyn, a Howard County police spokeswoman. "We have not been able to establish a motive. We've just gathered evidence that points to them being responsible."

According to police, they decided to carry out the crime on Thursday after discussing it through "electronic communication" for the past two months. Arnold left open a sliding glass door, allowing Bulmer to slip in around 4 a.m., police said.

Howard County Executive Ken Ulman said he was "shocked and saddened" by Lane's death, calling him a "significant and thoughtful voice in the Howard County business and political community."

Lane worked in commercial real estate and was well known through his blog, "Tales of Two Cities," where he wrote about real estate and other county issues and often referred to his daughter as "peanut." He also hosted a podcast.

Baltimore City Councilman James Kraft, a friend, called Lane "one of the best people I know — everybody loved the man."

"Morgan was his life," Kraft said. "He loved that girl. He just loved that girl. ... Everything I know about Morgan and Dennis is that they had a great relationship. … My whole knowledge is that she loved her father and he loved her."

Relatives of Bulmer and Arnold could not be reached or declined to comment Friday.

Bulmer and Arnold posted frequently on social media. The pair often wrote to each other, expressing their mutual affection — the profile picture on a Facebook page that's linked to her father's page and that friends confirm was hers shows Pegasus and in orange letters reads, "I love Jason."

Clay Bleyer, 14, also a freshman at Mount Hebron, said Arnold and Bulmer hung out mostly with one another — they "just did their own thing" —and he often saw them laughing together.

"The only person I saw her with in the halls with was Jason," he said. "They would always hold hands in the hallway, and Jason would always wait outside her classes for her."

Sarah Fuss, a Mount Hebron freshman who said she was perhaps Arnold's closest friend, was stunned to learn of the allegations.

"I'm freaking out about it," said Fuss, who lives in Arnold's Ellicott City neighborhood, Taylor Village.

While Fuss said she has known Arnold for about eight years and was taking two classes with her this year, Fuss didn't know Bulmer well. Paige Fuss, Sarah's mother, said the two girls had gone hiking together recently.

"This has been a terrible blow to everyone. It's a very, very sad situation," she said. "Dennis was a very good person, a very good father. We're just all so devastated."

Taylor Village was quiet Friday afternoon, with few vehicles driving through except a mail truck. At Lane's house on Winding Ross Way, which meanders through cul-de-sacs, a white SUV remained parked in the driveway.