Now a story we've followed very closely here at Crime Watch Daily: A mystery man in a mask and a murdered fitness instructor. Breaking new developments in the shocking murder of fitness trainer Terri "Missy" Bevers, killed on April 18.

Federal agents are now on the investigation. Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives have been seen investigating the crime scene with a K-9 unit.

Crime Watch Daily and Dallas affiliate KDAF have been following the killing that has shocked north Texas.

Midlothian Police believe a figure seen on camera in a SWAT team uniform ambushed Bevers when she arrived for her early-morning boot camp class.

We're learning there is only one place in town where the suspect might have bought the 5.11 brand of tactical equipment popular with police: Jeremy Washington's Code Blue Police and Security Supply Store.

"We sell a lot of 5.11 gear: Boots, flashlights, batons, handcuffs," said Washington.

Monday, April 18, 2016:

3:58 a.m. The mystery person is seen in the hallways of the local church.

4 a.m. Missy Bevers arrives with her gear to set up for her class.

Then the video mysteriously goes to black.

Around 5 a.m., Missy's students arrive to find a horrifying scene: She's been murdered.

Cops find broken glass on the floor. Nothing is missing.

Missy's husband Brandon is baffled. KDAF says he was seen walking into the police station late Thursday.

"It was a shoddy amount of clothing to look like some type of enforcement officer, it wasn't real tactical clothing," Brandon said.

And Jeremy Washington says not just anyone can buy a cop uniform.

"The first thing we're going to do is ask you for credentials, and then as you present your credentials of police, security, constable, sheriff, that gives you authority to buy what you need," said Washington.

The real cops aren't revealing a motive for murder. They originally thought Missy surprised a burglar, but they are no longer convinced that's what happened.

A search warrant obtained by Crime Watch Daily reveals Missy died from a head wound. Cops believe the assailant used an "unknown instrument."

Police now believe the suspect could even be a woman, saying in a new press release: "The department's desire is for the public to analyze the video to see if the walk and stature or the suspect is recognizable."

Missy Bevers was just 45 years old, the mother of three young girls. Her husband is still in shock.

"I haven't had a lot of time to get emotional about this yet, I've been dealing with the immediate needs of my children," said Brandon Bevers.