What we know about the killing of pregnant Maryland 'teacher of the year' Laura Wallen

— -- Investigators are awaiting autopsy results as they work to piece together details of what led to the killing of a pregnant Maryland high school teacher found dead nine days after being reported missing.

The Montgomery County Police Department announced Wednesday night that Laura Wallen's boyfriend, Tyler Tessier, was arrested and charged in her slaying.

The motive and cause of death are unknown, police said.

A judge in Rockville District Court ruled this afternoon that Tessier be held until trial without bond.

"I do think that you are a danger to the community," the judge told Tessier, who appeared via video monitor.

His defense attorney, assistant public defender Victoria Kawecki, argued he be granted bond because he had no prior criminal history.

Kawecki's office declined to comment on the case Thursday.

Tessier was charged with first-degree murder, altering physical evidence and making a false statement to police, according to court documents.

Wallen, 31, of Olney, Maryland, was a social studies and law teacher at Wilde Lake High School in Columbia, where she was awarded “Teacher of the Year” in 2016. She had been "super-excited" about the new school year, her father, Mark Wallen, told reporters Wednesday.

She was absent on the first day of school, Sept. 5.

A prosecutor described Wallen in court today as a “very dedicated and involved teacher.”

Wallen’s sister informed detectives that she was four-months pregnant with Tessier's child, according to the Montgomery County Police Department. It’s unclear whether they lived together.

Police last week discovered her 2011 black Ford Escape parked in a gated apartment complex almost directly across a highway from the high school.

Members of the community handed out and posted paper fliers around Howard and Montgomery counties over the weekend showing the blond-haired, blue-eyed teacher with the words "MISSING" in red.

“She’s always willing to put her students first, so I know if one of us was in this situation, she would’ve been head-on attacking it and in the streets just like we are,” Saquan Maxwell, who organized the community effort, told ABC Washington, D.C., affiliate WJLA-TV Saturday.

“My heart goes out to her wherever she is,” said Madison Pearson, who told WJLA she had Wallen as a teacher in middle school and high school.

Where authorities found her body

The Montgomery County Police Department on Wednesday afternoon searched the perimeter of a wooded area in Damascus, where investigators allege that Wallen's boyfriend had taken several trips recently to an acquaintance's property.

Detectives came across freshly dug ground in a secluded part of a field there. Cadaver dogs indicated the spot and Wallen's body was discovered in a shallow grave, officials said.

Tessier was arrested and charged with first-degree murder, Montgomery County Police Department Chief Thomas Manger told reporters at a news conference Wednesday night.

The owner of the property where Wallen's body was found has no involvement in the case and Tessier is the only suspect, Manger noted.

"It is with a heavy heart that we share the news that Wilde Lake High School teacher Ms. Laura Wallen was found deceased tonight by Montgomery County Police,” the Howard County Public School System said in a statement Wednesday. "Please keep Ms. Wallen's family in your thoughts."

Where she was last seen

Police said Tessier was the last-known person to have been in contact with Wallen. The last-known transaction in Wallen's financial accounts was a debit card purchase at a Safeway grocery store near her home in Olney Sept. 2 between 8:30 and 9:30 p.m. local time.

Police said a review of surveillance video showed the couple as they made a purchase together.

Investigators suspect she was killed the next day, according to Manger.

Wallen contacted her sister in a text message Sept. 2, saying her boyfriend had taken her on an "adventure" to a field in the rural Damascus area, according to the Montgomery County Police Department.

The sister told Wallen to take a picture, and she did, Manger said.

Police later obtained that photo and matched it to the property where Wallen's body was located, Manger added.

Investigators said Tessier had texted an acquaintance late on Sept. 3 asking for a ride to Baltimore, saying he needed help to "clean up a mess." But the acquaintance declined to assist, Manger said.

Wallen's family received text messages from her cellphone Sept. 4, according to Manger.

Investigators determined that Tessier had sent those messages, which he allegedly acknowledged during questioning, Manger said. It's unclear what the messages contained.

What her boyfriend allegedly told investigators

Tessier allegedly provided information to detectives and made admissions that led them to suspect his involvement in Wallen's death, according to the Montgomery County Police Department.

Police say that Tessier drove Wallen's car to the apartment complex in Columbia, where the vehicle was later located. He allegedly told police that he had removed and disposed of the front license plate, as well as throwing away Wallen's driver's license and cellphone in a dumpster.

Detectives located another acquaintance of Tessier who said the suspect had called her to give him a ride from the apartment complex in Columbia. Tessier allegedly asked the acquaintance to lie if police ever asked her about picking him up there.

He also allegedly told detectives that he is engaged to another woman.

Tessier spoke at a news conference Monday, where he told reporters he had known Wallen for about 10 years. At one point, he held the hand of Wallen's mother, Gwen Wallen, as they appealed to the public for help in locating her.

While speaking to reporters Wednesday night, Manger said Tessier was already a person of interest at the time of Monday's news conference, after police identified "a couple of inconsistencies in information that he'd given us."

Manger said Tessier's appearance at the news conference was a "calculated decision" made by police and Wallen's family.

"It was a calculated decision made by detectives to have Tessier attend the event and speak," the Montgomery County police chief told reporters. "It was done with the approval and knowledge of the victim's family."

Wallen's father spoke at a press conference on Thursday, calling Tessier "a monster" and "a liar," and saying he had deceived his daughter "their entire existence."