Jason Bulmer and Morgan Lane Arnold

Authorities released booking photos of Jason Bulmer and Morgan Lane Arnold. (Howard County Police / May 13, 2013)

The 19-year-old man charged with fatally stabbing Dennis Lane allegedly told investigators that his girlfriend had instructed him to kill her father and his fiancee, specifying the number of times each was to be stabbed in the throat — 10 for him and 15 for her.

Jason Anthony Bulmer charging documents

In a conversation at school hours before the Ellicott City blogger and businessman was killed, Jason Anthony Bulmer said, 14-year-old Morgan Lane Arnold told him "I don't know what I'll do if you don't do it tonight," according to charging documents released Monday.

Bulmer sent her a picture of a kitchen carving knife before he entered through a sliding glass door that she had left unlocked, police said. "Arnold gave a reply that indicated to Bulmer that this knife was satisfactory," Det. Donald Guevara wrote in the court papers.

The documents offer the first indication that Denise Geiger also was targeted in the attack early Friday on Lane, which shocked local residents and those who knew Lane and his daughter. Arnold and Bulmer are both charged with murder, and made their first court appearances Monday. Both will continue to be held without bail.

Morgan Lane Arnold charging documents

According to court records, Arnold had a rationale for killing Lane and Geiger. "I have my reasons and I'll tell you later," she allegedly told Bulmer, who relayed the conversation to investigators asking about the difference between the number of times each victim was to be stabbed. Afterward, Arnold promised the pair would run away to California, Bulmer allegedly told police.

But Geiger survived, and the charges don't indicate she was harmed. She called police from the Ellicott City home she owned with Lane and reported her fiancee was struggling with Bulmer. By the time police arrived, according to the documents, Lane was dead in one upstairs room, Bulmer and Arnold were in another, and Bulmer's hands and clothes were bloodied.

The charging documents refer to a string of communications between the two students in the days and hours before the killing of Lane, a prominent community member in Howard County.

Police said Bulmer gave them an account of the plot after he was arrested and waived his right to remain silent. Even before being transported to police headquarters, Bulmer told police at the home that he had killed Lane and that Arnold had told him to do it, according to the documents.

Bulmer also told police the plot had been unfolding for months, but "communications concerning the murder became more frequent within the past several weeks," the detective wrote.

In one of the more chilling allegations in the documents, police said Arnold told Bulmer there weren't any sharp knives at her home.

The two Mount Hebron High School students appeared separately in court Monday via video link from the Howard County Detention Center.

Arnold will remain in custody after her public defender waived her right for a bail review hearing. She appeared in a yellow jumpsuit and spoke little. Asked her name by the judge, she replied, "Morgan." Her face reddened as the hearing went on, her arms shackled and folded in front of her.

Arnold's mother, Cindi Arnold, was in the front row of the courtroom but declined to speak to reporters. A public defender assigned to Morgan Arnold's case could not be reached.

In a previous statement, Cindi Arnold described her daughter as a "special-needs child." Arnold is scheduled to have a preliminary hearing in the case May 24.

Complete coverage: Murder of Howard Co. blogger Dennis Lane

Bulmer, who appeared in a sleeveless blue smock that revealed a large tattoo on his right biceps, was denied bail by District Judge Mary Reese. A prosecutor described him as a danger to the community, himself and witnesses in the case.

Bulmer's public defender described him as a sophomore in high school who lives with his mother and has few financial resources. His attorney also said he had moved to Maryland four years ago.

Gary Bulmer, Jason's father, who lives in Plymouth, Mich., and is divorced from the teenager's mother, described his son in an interview as a gentle young man who had trouble with schoolwork but with whom he has a good relationship.