"We've had such an outpouring of support coming from every direction," Bevers says

Brandon Bevers, the husband of the Texas fitness trainer found dead before her class on April 18, tells PEOPLE he knows things about the investigation that the public doesn’t and that he’s pleased with the direction of the investigation.

“I’m privy to some things that nobody is aware of, and I’m impressed with them,” he tells PEOPLE. “I really can’t talk about anything in terms of the investigation because it’s ongoing. But I have quite a bit of faith in what they’re doing.”

Midlothian Assistant Police Chief Kevin Johnson tells PEOPLE that he can’t comment on specifics of the investigation, including whether an arrest is imminent or not, but they “continue to work through leads.”

Terri “Missy” Bevers was scheduled to teach a Camp Gladiator class at the Creekside Church at 5 a.m. the morning of her murder. Surveillance video shows her entering the building, after which a suspect, dressed in police tactical gear, is seen walking in carrying a hammer. According to police, Bevers died of “multiple puncture wounds” to her head and chest consistent with what the suspect on surveillance was seen carrying.

She was found by one of her Camp Gladiator students, who called 911.

In a search warrant released on May 5, police said they have reason to believe Bevers and her husband were having “an ongoing financial and marital struggle as well as intimate/personal relationship(s) external to the marriage.” They say they’ve recovered messages on Missy’s devices that are “flirtatious” and “intimate.”

While Brandon Bevers says he “is not in a right state of mind” to talk in detail about the tragedy, he did say that the couple’s three daughters, ages 8, 13 and 15, are holding up well.

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“We’ve had such an outpouring of support coming from every direction,” he tells PEOPLE. “We’ve been bombarded with blessings.”

One setback he did mention involves the family’s health insurance. Because Missy was the primary person listed on the policy and is deceased, he says he was recently told his insurance is longer valid.

“No one told me. I was going to use that for counseling services for the girls,” he says.

‘Mother-in-Law: Details of Flirtatious Messages ‘Knocked Us Down a Little Bit’

In a separate phone interview on Tuesday, Marsha Tucker, Brandon’s mother and Missy’s mother-in-law, tells PEOPLE that the details about Missy’s “flirtatious” messages “knocked us down a little bit.”

Tucker says she wasn’t aware the couple was having financial or marital problems.

“I mean, as bad as it is on the girls, especially the older ones, for Brandon to lose his wife to murder and then find out about the flirtatious remarks to other people has got to be devastating to him,” she says. “I mean, enough’s enough here.”

Tucker has written two open letters to the killer on Facebook. She tells PEOPLE that she wrote them in part “for everybody to know, especially after last week, that we love her.”

“We know she wasn’t perfect; none of us are perfect,” she adds. “But we love her no matter what.”

Tucker is well aware of all of the rumors about the killer’s identity. As for speculation that it was her ex-husband, Randy Bevers, she says, “He was in California, and they’ve proven that. He and his wife had to fly back the next day.”

Mother-in-Law Says Bevers Was ‘Tender-Hearted’

Tucker describes her daughter-in-law as “a very caring person. She was tender-hearted; she’d cry if she heard about an animal getting hurt.”

As for her life as a mom, “If she wasn’t doing her camp stuff, she was running the girls around here and there. They’re all in sports, and it’s taking three of us to do her job now.”

Missy became passionate about getting into shape about two years ago, Tucker says, adding that it was around that time that she became certified as a trainer.

But Tucker has mixed feelings about Camp Gladiator, noting that she doesn’t even like to say the name. Asked why, she replies, “I guess because it took so much of her life, and then it took her life.”

Recalling the last text she got from Missy, Tucker fights back tears as she describes it: “She’d gone to Austin for a Camp Gladiator meeting, so I took Brandon in for minor surgery,” she recalls. “Missy texted to say, ‘Thank you for taking care of him. I love you.’ That was the last text I got. I loved her, and she loved me.”

Tucker believes the police “have a good handle” on the case at this point: “I think they’ve got it under control, let’s put it that way. I’m confident that it will be solved, but not soon enough for me.”

As for how her granddaughters are doing, Tucker says, “On the whole, they’re doing good. There’s a bubble of God’s grace around them. It’s amazing.”

She sighs heavily as she recalls the morning of the murder, when she had to drive to the Bevers’s home after hearing the news about Missy. The girls were home alone, sleeping.

Tucker waited for two other relatives to arrive “because I didn’t have enough arms to console them,” she says. “We had to wake them up and tell them, ‘We don’t know what happened, but your mama’s gone.’ “