The missing pregnant teacher from Montgomery County was found dead on Wednesday, according to Montgomery County police.
Police say that Tessier drove Wallen's auto to the apartment complex in Columbia, where the vehicle was later located.
The Montgomery County Police Department previously said in a news release that Wallen's family received the text on the morning of September 4.
Wallen - who was four months pregnant - vanished last week after she contacted relatives in a text message, authorities said.
'Laura, if you are listening, it doesn't matter what's happened, it doesn't matter what type of trouble, there is nothing we can't fix together - myself and your family, ' Tessier said at the conference. He said the acquaintance declined to help.
Her father Mark Wallen went to her condo but could not find her and became anxious for her safety.
Tessier had participated with Wallen's family in a news conference Monday about her disappearance.
Investigators determined that Tessier had sent those messages, which he allegedly acknowledged during questioning, Manger said. They went to the home on the neighboring plot and got access to that field, where cadaver dogs led police to find Wallen's body in a shallow grave.
"The decision to allow him to participate in that news conference was a calculated decision made by the detectives in this case for the expressed goal of hearing what he had to say", Manger said, noting that police had the family's approval. Police are now telling WUSA9 that they were treating Tessier as a "person of interest", before the press conference even began. "We had a real sense of dread that this was the way it was going to end up".
The cause of death is unknown, Manger said.
Her parents and boyfriend offered a $25,000 reward for information on her whereabouts on Monday.
Despite being Wallen's boyfriend, police discovered that Tessier was also living with another woman.
Wallen's father, Mark Wallen, had said he became certain something was awry when he called Wilde Lake High School on Tuesday morning to check if his daughter had arrived and was told she had not.
Manger said Tessier's appearance at the news conference was a "calculated decision" made by police and Wallen's family.
He said prosecutors would determine whether to also charge Tessier in the unborn baby's death.
Community members gathered in mourning Wednesday night at Wilde Lake High School, where Wallen had been named Teacher of the Year in 2016.
The "Gathering of Hope" event scheduled for Wednesday evening has been canceled, the school system said.
Students held a candlelight vigil in Wallen's honor Wednesday night, and school district officials were supplying counselors at the high school and at Murray Hill Middle School, where she previously taught.
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