FARMINGTON — Lizzette Robinson, 5, clutches her dead mother's backpack and sobs for her to come home.

Dayton Robinson, 14, has hardly left his room since his older sister was killed.

Tammy Robinson hides in her room so her grandchildren can't see her cry for her daughter.

Brandy Robinson, 29, was stabbed to death in a rural area south of Farmington on June 22. Now her family, who have lived in San Juan County for 40 years, are struggling to deal with the death. They said on Tuesday that they can't comprehend how someone could kill a young mother.

The San Juan County Sheriff's Office said one of Brandy Robinson's ex-boyfriends, Michael Graham, is a "person of interest" in her death. The family said that people who know useful information about the case are not cooperating with the investigation.

On Friday, the sheriff's office arrested Graham, 40, on suspicion of tampering with evidence and possession of firearms and destructive devices by a felon. Deputies said they found Graham with illegal weapons when they searched his truck and bedroom as part of the homicide investigation.

Sheriff's office Lt. Cory Tanner said the investigation is ongoing, and detectives are still gathering information from people who may have knowledge about the circumstances of Brandy Robinson's death.

"I'm confused," said Tammy Robinson. "I don't understand how somebody could do something like this. I'm angry. I'm so angry. I want to go back to two weeks ago and go get her and not let her out of my sight."

Brandy Robinson's aunt, Connie Chavez, described her niece as energetic. Chavez said her niece often hiked to the top of a mesa near the family's property -- she lived in a mobile home on her parent's three-acre property in Bloomfield -- and searched for rocks. She coined goofy nicknames for her relatives.

Brandy Robinson is seen in her Facebook profile picture posted in June 2012. Robinson was found stabbed to death south of Farmington on June 22.
Brandy Robinson is seen in her Facebook profile picture posted in June 2012. Robinson was found stabbed to death south of Farmington on June 22. (Facebook)

"She loved to color her hair. She had some wild in her hair," Chavez said. "She loved life. She loved to write poems and draw."

Brandy left behind three children -- Alissa, 3, Lizzette, 5, and Destiny Robinson, 9. She also is survived by three younger brothers, Dayton, 14, Devin, 22, and Donald, 26.

Tammy Robinson said her daughter struggled with drugs. In 2006, she was arrested on suspicion of possession of cocaine. Her mother said that Brandy Robinson had been clean for several years until she began hanging out with a "rough" crowd in the months before her death. That created tension in the family, Tammy Robinson said.

"I was giving her tough love, trying to get her off the drugs," Tammy Robinson said. "She had troubles with drugs, but she had gotten clean. She had been clean for four or five years, and then she got back on it."

She said that her daughter knew she had a problem and was determined to improve her life. Brandy Robinson talked to her mother about leaving New Mexico to get away from the people she used drugs with, Tammy Robinson said.

Tammy Robinson said she heard from her daughter for the last time on June 12. Brandy Robinson sent her mother a text message that said she loved her.

On June 13, Brandy Robinson was assaulted by her current boyfriend, her mother said. Sheriff's office officials confirmed that there was a domestic violence call on June 13 concerning Brandy Robinson and her boyfriend.

The next day, Brandy Robinson left her two youngest children with an acquaintance. Her eldest daughter lives with her grandmother.

On June 14, Brandy Robinson posted on her Facebook page that she wanted to smoke marijuana because she was stressed. She also wrote that she wanted a boyfriend who really loved her. Later that day, she wrote that she wanted to jump off a cliff.

The next day she posted a message that read she was "enjoying the cloudy day and no stress."

On June 14, Tammy Robinson picked up her grandchildren and was told her daughter was with Graham, who has a history of domestic violence against Brandy Robinson, according to court documents. He has been convicted of multiple felonies, including aggravated assault with a deadly weapon in 2000.

On the evening of June 22, three detectives told Tammy Robinson and her husband, Gary, that their daughter was killed.

Her body was found south of Farmington, though investigators haven't told the family the exact location.

What happened in Brandy Robinson's final days are unclear.

The people who were with her in her last week have been uncooperative and have misled the investigators at times, said sheriff's office Capt. Brice Current. They may have criminal charges brought against them, he said.

"People who were supposed to be her friends won't say anything. If you know something, just come forward and tell the detectives the truth," said Tammy Robinson. "I hope their guilt just eats them up because it's killing us."

The Robinson family has organized a memorial for Brandy Robinson at 3 p.m. today at Kiwanis Park, 3540 E. 30th St. in Farmington.

The sheriff's office is asking anyone with information on Brandy Robinson's death to call Detective Candice Montoya at 505-334-7049. Those who wish to remain anonymous can call San Juan County Crime Stoppers at 505-334-TIPS (8477).

Ryan Boetel covers crime for The Daily Times. He can be reached at 505-564-4644 and Follow him on Twitter @rboetel on Twitter.